If you could build a new shop, being reasonable here, what dimension would you build? I have thought about this and have not arrived at an answer yet, as there are a number of considerations. What height would you put the ceiling at? Standard eight feet, or would you go ten?
Cost is a major part of the equation, but should not be the top priority as once it is built, you will obviously live with it for a long time. How about rooms inside it? Just one big open room, or would you include a separate finish room?