"Oh I would never dream of assuming I know all Hogwarts' secrets..."
     -- Albus Dumbledore

It is not possible to create an accurate floorplan or map of Hogwarts (Sch1) because rooms and staircases move around a lot. 

There were a hundred and forty-two staircases at Hogwarts: wide, sweeping ones; narrow, rickety ones; some that led somewhere different on a Friday; some with a vanishing step halfway up that you had to remember to jump¹. Then there were doors that wouldn't open unless you asked politely, or tickled them in exactly the right place², and doors that weren't really doors at all, but solid walls just pretending. It was also very hard to remember where anything was, because it all seemed to move around a lot. The people in the portraits kept going to visit each other, and Harry was sure the coats of armor could walk. (SS8)

Dungeons and sub-levels:

• Potions classroom
• large enough to accomodate a double class (about twenty cauldrons)
• "Potions lessons took place down in one of the dungeons. It was colder here than up in the main castle, and would have been quite creepy enough without the pickled animals floating in glass jars all around the walls." (SS8)
• icy cold water pours from a gargoyle's mouth into a basin in the corner
• you can see your breath in this room during the winter months
• Snape's office and private stores
• adjacent to classroom
• filled with bizarre creatures in jars, his own private stores of potion ingredients, located next to his dungeon classroom
• Slytherin dungeon common room
• hidden door in a blank stone wall, opens by password
• low ceiling, greenish torchlight
• Dungeon Five
• some third year accidentally plastered frog brains all over the ceiling in this dungeon, which suggests that it is used for making potions (CS8)
• other dungeons, including one large enough for a Deathday party
• kitchens
• located directly beneath the Great Hall, equal in size
• preparation tables directly under the tables above
• staffed by over a hundred house-elves
• corridor with door to kitchens
• pictures on the wall, mostly of food
• down a flight of stone steps into a  broad stone corridor, brightly lit with torches
• this corridor also leads to the Hufflepuff common room
• the Chamber of Secrets and passageways leading to it
• the chamber of the Philosopher's Stone and passageways leading to it
• Hufflepuff common room (or at least Diggory heads down the kitchen stairs as he heads off to his common room)

Ground Floor: (Atlas: map of ground floor)

• Entrance Hall 
• Double oak front doors, opening to the west (PA21). Large, cavernous room, lit by torches, with ceiling so high it's barely visible. Wide marble staircase opposite the front doors (east wall) leads up to first floor. Double doors to the right (south wall) lead into the Great Hall. On the east wall are two doors, one on either side of the staircase. To the north of the staircase is a door leading down a flight of steps to the first dungeon level. To the south is a door leading to the Hufflepuff common room and the kitchens. On the left (north wall) is a door leading to a smaller antechamber where First Years wait to be sorted.
• Great Hall
• Vast chamber with an enchanted ceiling which mirrors the sky outside. Four long tables for the four houses. Closest to the doors from the Entrance Hall is Slytherin, then Ravenclaw, Hufflepuff, and next to the far wall, Gryffindor (this order may possibly be reversed, depending on how you orient the room to the entrance hall). The teachers sit at the High Table, a table on a raised platform at the front of the room. 
• A door behind the staff table allows a person to enter the Great Hall from outside without going through the main entrance (Hagrid enters this way to the welcoming feast in GF); it isn't clear if this is the same door as the one leading into the antechamber.
• there are windows into this room from the lawn outside (CS5)
• There is a smaller antechamber connected to the Great Hall, door behind the teachers' table,  with a fireplace and many portraits (including that of the Fat Lady's friend Violet) off the Great Hall (GF
• small chamber 
• located off the Entrance Hall, opposite the Great Hall
• where first years wait to be sorted
• broom closet
• located off the Entrance Hall
• Harry and Ron locked Crabbe and Goyle in it (CS12)
• Hermione and Harry hid here while using the Time Turner to wait for themselves to pass through the Entrance Hall (PA21)
• staff room 
• long panelled room
• mismatched, dark wooden chairs
• large wardrobe, sometimes inhabited by a boggart
• located off the Entrance Hall (SS16)

• Muggle studies classroom
• to get to her Muggle Studies exam, Hermione stops at the first floor while Ron and Harry go on (PA16)
• McGonagall's office
• up the marble staircase and down a hallway, on the first floor (PA
• Hospital Wing [3]
• lots and lots of beds with white sheets
• Madam Pomfrey's office
• privacy screens
• bedpans (since Ron has to scrub them for detention) (PA

• Moaning Myrtle's bathroom (out of order)
• empty corridor with stone gargoyle the entrance to Dumbledore's Office [4]
• Defense Against Dark Arts professor's office (sometimes 3rd floor)
• faces south (GF, Moody looks out and sees Durmstrang ship)
• Lockhart - vanity pictures of himself
• Lupin - grindylow tank, creatures for use in class, tea things
• Moody - Foe-Glass, Dark Detectors, seven-lock chest

• statue of humpbacked witch with secret passage to Hogsmeade
• forbidden corridor where Fluffy guarded the trapdoor to the hiding place of the Philosopher's (Sorcerer's) Stone
• trophy room
• armor gallery (adjacent to the trophy room)
• Charms classroom, down the Charms corridor

• fourth floor corridor - Harry encountered Peeves here (GF
• there is a landscape painting here which the Fat Lady was seen running through after Sirius Black attacked her (PA8)
• there is a secret passageway out of Hogwarts behind the mirror on the fourth floor, but it's caved in and completely blocked. (PA10)

Fifth Floor

• statue of Boris the Bewildered
• Prefect's Bathroom
• white marble
• large pool-like tub
• a hundred taps giving water plus various bubble bath, etc.
• picture of a mermaid on the wall
• 4th door to the left of the statue of Boris the Bewildered
• password: "pine fresh"

Seventh Floor

• Gryffindor common room (base of Gryffindor Tower)
• begins on the seventh floor
• common room with squashy armchairs, a fireplace, tables
• entrance behind a large painting of a Fat Lady in a pink silk dress in a corridor on the seventh floor. If you know the right password to tell her, she opens to reveal a round opening in the wall.
• dormitories - one boys' and one girls' per year for a total of fourteen -  with four-poster beds - round rooms with windows
• Divination classroom
• base of North Tower
• round room
• access is by means of a ladder through a ceiling trap door from the room below
• oppressive fire with a copper kettle that gives off sweet-smelling fumes
• walls lined with shelves: tea cups, crystal balls, decks of cards, etc.
• small round tables, squashy armchairs and little poufs
• at least one window which Harry opened just a crack to let fresh air into the room (GF
• Flitwick's office 
• thirteenth window from the right of the West Tower

• Astronomy Tower (tallest tower)
• where they have Astronomy class every Wednesday night at midnight
• handy for releasing baby dragons in the dead of night
• Dumbledore's residence and office
• round room with windows
• entrance is through a secret door behind a stature of a gargoyle on the second floor (GF28), the password for which seems to be the names of sweets that Dumbledore likes
• once in the door, you ride on a spiral wooden stairs that moves slowly upward
• Phoenix on a stand, Sorting Hat, Gryffindor's sword, cupboard with Pensieve in it
• portraits of previous Headmasters and Headmistresses
• desk and chairs
• "It was a large and beautiful circular room, full of funny little noises. A number of curious silver instruments stood on spindlelegged tables, whirring and emitting little puffs of smoke. The walls were covered with portraits of old headmasters and headmistresses, all of whom were snoozing gently in their frames. There was also an enormous, claw-footed desk, and, sitting on a shelf behind it, a shabby, tattered wizard's hat -- the Sorting Hat." "Standing on a golden perch behind the door was a decrepit-looking bird..." (CS12)

 
• North Tower
• Trelawney's residence and the Divination Classroom (PA16)
• Gryffindor Tower
• Harry's dormitory room is at the top (GF12)
• Atlas: Harry's dormitory room
• West Tower
• the Owlery is located at the top of this tower (GF15)

• Hufflepuff common room and dormitories
• located down the staircase to the right of the main staircase in the entrance hall
• Ravenclaw common room and dormitories
• location and description unknown
• library
• tens of thousands of books, thousands of shelves (SS12)
• Filch's office
• filing cabinet with records of the misdeeds of students, including an entire drawer for the Weasley twins.
• chains and manacles (not used these days but kept polished just in case)
• cabinet full of confiscated magic items
• desk and chairs
• lots of forms to write up malafactors
• smells vaguely of cooked fish
• magical chamber pot room
• "Oh I would never dream of assuming I know all Hogwarts' secrets, Igor," said Dumbledore amicably. "Only this morning, for instance, I took a wrong turning on the way to the bathroom and found myself in a beautifully proportioned room I have never seen before, containing a really rather magnificent collection of chamber pots. When I went back to investigate more closely, I discovered that the room had vanished.  But I must keep an eye out for it. Possibly it is only accessible at five-thirty in the morning. Or it may only appear at the quarter moon - or when the seeker has an exceptionally full bladder." (GF23)
• classrooms
• History of Magic
• blackboard through which Binns enters the room
• Transfiguration
• Defense Against the Dark Arts classroom
• has windows
• had an iron chandelier until Neville was hung from it by his ears by pixies and it broke off the ceiling (CS

NOTES
1 - Harry finds himself stuck in just such a staircase on his way back from the Prefects' Bathroom. He is almost caught by Snape and Filch but he is rescued by Moody (GF25). Neville kept forgetting this particular step and had to be pulled out of it more than once.

Neville’s foot had sunk right through a step halfway up the staircase.  There were many of these trick stairs at Hogwarts; it was second nature to most of the older students to jump this particular step, but Neville’s memory was notoriously poor. Harry and Ron seized him under the armpits and pulled him out, while a suit of armor at the top of the stairs creaked and clanked, laughing wheezily (GF12).

(Hermione) seized his arm again, pulled him in front of the picture of the giant fruit bowl, stretched out her forefinger, and tickled the huge green pear.  It began to squirm, chuckling, and suddenly turned into a large green door handle. Hermione seized it, pulled the door open, and pushed Harry hard in the back, forcing him inside. (GF21)

4 - Harry runs into the castle to find Dumbledore when Mr. Crouch accosts him and Viktor near the forest:

Harry tore up the stone steps, through the oak front doors, and off up the marble staircase, toward the second floor.
Five minutes later he was hurtling toward a stone gargoyle standing halfway along an empty corridor. (GF28)