What ever size you decide on, it seams, will become to small in a short period of time. I have 2 rooms one is 12 X 20 The other is 15 X15, both packed full, I really need to clean out a lot of this stuff. I would first decide what size furniture you have to put in there, make scale cutouts and arrange them on graph paper move it all around until you are happy with the layout. Than add a couple of feet in each direction, should give you a good starting point to decide on going larger or smaller. Do you want any built in's? make allowance for doors opening, windows, are you having a 1/2 bath put in? A counter for a pot of coffee? Under counter frig? Do you have a long arm? good luck and enjoy the process. let us know what happens.