The 'Floor Area' of a building is a measure* of the amount of useable space in a building (and its attachments) at the final stage of construction. It is measured in square metres.
The boundary of the floor area is delineated by the external perimeter of the exterior walls of the building, but the area under unenclosed verandahs, carport etc, attached outside the exterior walls is excluded.
* According to the Australian Bureau of Statistics