Many moons and ages ago I worked as a staff appraiser for FHA. In those days when there were only staff appraisers and no panel of fee appraisers, FHA had strict, stringent control over it's appraisers. It was mandated that all condo appraisals could not be completed unless the condo documents were examined. And, yes, in those days, the condo developments did have them available for us to see. What I learned through this is that each and every plan in the development is spelled out with the "legal" square footage indicated in the documents. Of course, being a condo, this square footage is the interior air space (simplified definition). Even though I rarely see these documents these days, I usually measure the condo for a general layout and arrangement, and place a disclaimer stating that for consistency purposes, since the subject is a condo, reliance has been placed on the tax square footage for living area. I have never had any questions or negative feedback from the lenders when using the approach.