Michael, I would create a worksheet. Cell one would calculate the floor area. Cell two calculates the length of the exterior walls multiplied by their finnished width (i.e. 4.5 in., 6.5 in. or ?). Cell three calculates the length of the interior walls multiplied by their finnished width. Cell four subtracts the area of the walls from the floor area.(Make sure your products are compatable before you combine them, i.e. sq ft.or sq. in.) You can make this worksheet a part of your drawing template so it will always be available. Just click on the worksheet to see your info.