You can make a very simple schedule to extract this information from a Zone or Fill.
Depending on what building codes your working with there may be some rules for how Area calculations must be done.
FOR THE PURPOSE OF CALCULATING THE "DESIGN OCCUPANT LOAD" AREAS ARE CALCULATED AS FOLLOW:
FLOOR AREA, GROSS: The floor area within the inside perimeter
of the exterior walls of the building under consideration,
exclusive of vent shafts and courts, without deduction for corridors,
stairways, closets, the thickness of interior walls, columns
or other features. The floor area of a building, or portion
thereof, not provided with surrounding exterior walls shall be
the usable area under the horizontal projection of the roof or
floor above. The gross floor area shall not include shafts with
no openings or interior courts.
FLOOR AREA, NET: The actual occupied area not including
unoccupied accessory areas such as corridors, stairways, toilet
rooms, mechanical rooms and closets.
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