If the listing and appraisal misrepresented the size of the garage, you  might have grounds to bring a legal action to recover (such as from the builder or developer) compensation, such as an amount representing the different in value between home as listed and home as is. You would almost certainly not have grounds to rescind the transaction--a garage that is somewhat smaller than listed is likely not "material" (or significant) enough to warrant rescission. You should speak with a real estate attorney to discuss a possible cause of action.