Most mediaeval castles where built to protect people and property. This makes security and defence a vital factor in a castle floor plan. All mediaeval castles are different and with different floor plans; however, most castles have the same basic features. Some factors that the original castle builders would consider when creating a floor plan are terrain, number of people the castle supports, supplies and the wealth of people building it.
Decide on the dimensions of the castle. The outside wall of the castle has to surround all the buildings inside. If the castle is going to have a moat it will need to be around the outside wall.
Draw the moat on the graph paper. Scale the size down to fit on the paper. Most castles are scaled down to 48 to 1. This scale uses 6.25 mm (1/4 inch) to represent 30 cm (1 foot).
Draw the outer wall. In mediaeval times, the moat was the first line of defence for a castle. The outer wall was the second line. The wall was thick stone and contained one or two gates. The gates contained the drawbridges to cross the moat. Place guard towers at the outer wall as part of the wall. These towers are placed at all corners, by the gates and at strategic points around the castle. The towers are round and normally one storey higher than the wall. The guard towers allow the guards to see for long distances and prevent surprise attacks on the castle.
Create an inner wall. All castles have small courtyards and marketplaces in between the outer wall and inner wall. The inner wall is built much like the outer wall. However the inner wall only surrounds the keep. Towers and gates appear on the inner wall as well.
Draw a box inside the inner walls for the castle's keep. A keep is the building in the castle. All the housing, dining and throne rooms are located in the keep. Place one tower in the centre of the keep and separate the keep into the separate rooms. The keep itself was normally several stories high, including a basement. Make a floor plan for each storey separately. The walls and moat only have to appear on the ground floor plan.
Add details to floor plan. Areas such as gardens and stables were often located between the inner wall and the keep. Add staircases and battle engines such as trebuchets and catapults.