how to measure:

• sketch out the existing layout including the location of all windows, doors and closets.
• measure each wall, corner to corner. record the sizes and locations of all openings and built-ins (doorways, pass-throughs, built-in bookcases, etc).
• start at one corner of the room, measure the distance from the corner to the outside edge of the window casing; from there to the opposite edge of the window casing; and so on to the opposite corner.
• continue this process around the room and note the measurements on your drawing.

also include:
• ceiling height for each room
• location of all power outlets
• height of windows and doors
• location of windows on each wall
• location of any wall or ceiling lights