If I understand your question, you just need to tell someone/advertise the usable square footage of a commercial building. No, a broker is not needed for a measurement. Often times, people will list the footage mentioned on the tax rolls and cite the "per county record/per tax assessor".
If it is for a loan, you may want to have the property surveyed and or inspected for a more accurate number but this is just to satisfy the bank/lender.
Also, confirmation of size is something that should be a part of any buyer's due diligence.
good luck, feel free to contact me if I can help further.
Nov 21, 2009