My Perspective
If it is finished similar to the other rooms in the house that are counted as GLA, has the same or similar amenities such as HVAC, I count it as GLA. We are in a moderate climate. Many folks convert garages. If they are good conversions, I count it as GLA. If they leave up the garage door with insulation between the wall and the exterior garage door, I do not but I do count it as finished area with a cost to cure for a garage reconversion. If the "Florida Room" is just as well finished as the other rooms counted as GLA, it is GLA to me. I do not depend on the assessor to tell me what it is. And, since we have a water table near the surface we have very, very, very few basements. We have lot's of "FROG's"(Finished Room over the garage). Assessors don't even know how big they are. I usually will only count a FROG as GLA if it is a 2 story and open to the second floor like the other rooms. However, if it is a one story, access is only through a stairwell from the first floor, it is not GLA but is a finsihed room that probably will have about the same value as GLA.