What does 400 cc mean in building plans?

400 cc means 400 dimension units from CENTER to CENTER

For example, on a building Plan View_you will see lines running thru the center of the walls, if you look at the dimension line located at the top or side of a drawing, you'll see numbers between those lines. this means that the drawing was set out without thickness, so the measurements are therefore center to center. In real space the room is smaller than the cc size by Two Halves of the wall thickness. hth