Just like with today's houses, the size and number of rooms inside medieval castles varied according to the owner's wealth. The first castles were built of wood and didn't last long, but were eventually made of stone for longevity and to withstand attacks. Most castles were made of stone by the 12th century. I've included the main rooms that would most likely be present in most castles.The Ground Floor Rooms typically contained the kitchen and storerooms. The First Floor housed the Great Hall, and the Top Floors contained the private chambers of the lord and his family.
The Lords and Ladies Chamber
The Privy Chamber
The Throne Room
Various rooms of varying sizes and shapes where located throughout the castle for storage of unused furniture and goods. Sometimes these larger store rooms under the main living area might have been referred to as the Undercroft room.
This was the guarded area at the entrance to the castle. Depending on the size and layout design of the castle, this may include the towers, bridges and complex walls protecting the entrance.
This was usually the courtyard out in the open sky, but within the main castle walls.
The Barracks or Mess Halls
Was a location that houses soldiers and knights. They had their living quarters as well as meeting rooms. Depending on the castle design, it may have been located as a wing extension of the castle or a separate quarters within the main walls of the castle.
"Castles" at http://www.castles.me.uk/
"Wikipedia" at http://www.wikipedia.com/