I can feel your frustration as a buyer in not being able to know the size of rooms when you are viewing listings. However, while many states show sq. footage in their listings Georgia is not one of them. Interior Sq. Ft. is not used as a marketing tool because the actual information is not readily available to agents. Appraisers do not measure interior footage for lender appraisals, only exterior, for both new and re-sell homes. Tax records tent to reflect this information, which may be inaccurate, depending on the appraiser doing the measurement. Usually an accurate sq.ft. measurement is only conducted for "cost" appraisals, which are required by insurers for replacement building.
New home builders may show a total sq.ft estimate for a home, (i.e. 2400 sq.ft) but as I said it is not a requirement for marketing their homes. As a couple of agents have mentioned, the listing services just recently added this area on the listing forms but I would suggest that this info can only be approximate. If you find a home that you would like to make an offer on you can always request your agent to visit the home and get specific measurements of rooms for your review during the due diligence period of your contract or offer.
Please feel free to contact me with any further questions. I would be more than happy to help.