Welcome to GJ, tmars. There are plenty of members here in the same planning stage as you. Feel free to browse around and see what others have done.
The big question is to decide how you want to use your shop - weekend mechanic, car rebuild, wood shop, metalwork, kit cars or planes, or just a man cave to hang out and drink a cold one while watching a game or big race. Each one has different needs toward the goal. One thing I have learned, you can't have enough electric or lighting. 30x40 is a nice size to work with.
Good Luck with your project.