No matter how big you make it ----it wont be big enough! My shed is 10x12, 2x6 studs, lots of plugs and lights, fully insulated and heated by a small electric/oil filled heater. Its too small!! I also have a 30x40 foot shop, divided in two. Work area is 18x30 with double sliding doors so I can open it up to use the whole shop area if needed. It has 12 foot ceilings, 2x6 studs, fully insulated, gyprocked and painted. Lots of plugs and lights and windows. Wood burning stove and another (bigger) electric/oil filled heater that keeps the work area from freezing up in the einter. When I had it built I didnt put in water and washroom---BIG mistake!! I should have had a guest suite built onto onr end (like a friend di with his) but I didnt and now the cost is likely too much. SO----make it as big as you can afford!!