Start with a tape measure, a pad and a pencil. You are almost there!
A. Room structure
Measure the ceiling height in from floor to ceiling. Start with the first wall on the left and work to your right around the room (corner to corner).
B. Locating Windows
Indicate window and door location and sizes. Indicate all breaks in walls by measuring from the corner to the outside edge of the moulding. Indicate all appliance locations and width, height, and depth
C. Switches, Pipes etc.
Measure to centerline of plumbing, ducting and outlets. Finally, double check all dimensions.