How are "Out Buildings" measured?

Are they measured by actual usable interior space or by foot print? Our covenants do not specify... They simply state "The out-building cannot exceed 900 square feet". We have a designer that is very crafty and says that if we are allowed 900 interior feet, he can really maximize our allowable space. I have to assume that it's interior since our neighbors are over 900 if you measure theirs outside.

Thanks

you may have found a loop-hole

but

for property tax purposes the measurement is outside dimensions/footprint

imo:

get a legal opinion