Depends. Sometimes I'll simply do a couple spot measurements and compared to the assessors dimensions if they are available. In some areas you can't even access the exterior of the building to measure it. Recently I tried to measure retail spaces in an older structure. None of the units were rectilinear and it was very difficult to take interior measurements because of all the junk. When I got back to the office and tried to figure it out, it just didn't make any sense. Generally we avoid measuring buildings unless requested by the client. Even then we are very reluctant to do it.