It all depends on what all you plan to have in your room. My room is about 20 x 40 and could be larger. There is a stairway and bathroom out of that as well. I have a hide-a-bed, recliner, entertainment center, bookcases, large table for scrapbooking, built in drawers along the stairway wall and under the west window where there is a kitchen sized sink. I also have an island for cutting with storage underneath. So, like others have said - make it as big as you can afford
