Assuming your spaces are bound by the interior face of the wall:
Get the bounding elements of the space,
Offset the matching location curve by the full thickness parameter value for walls with an exterior function,
offset the matching location curve by 1/2 of the thickness walls with an interior function.
Create new polycurves by the offset curves.
Get the area of the polycurves.
Write that value to a new parameter (ie: dynamo calculated area) for each space