Gross Building Area

Gross floor area is the total floor area contained within the building measured to the external face of the external walls. Construction floor area is the total space in a building, including things like exterior walls, permanent partitions, fire walls, and areas in attics and basements. Essentially, gross floor area is the usable space, while construction floor area is the total space.

Believe it is gross residential area divided by gross building area.

depends on the area and height of the building

Usually a fenced off area where construction is taking place.