Build as big as you can afford. If like me, it will fill up over the years with jacks, drill press, welders, lathe, Bridgeport etc. Stuff you never thought you needed. Make at least one part that you can heat, with the rest storage. The doors should be as high too. Think of the things you may carry or boom in on a chain without looking up. I came close to hitting the 12' doors many times. Good luck.