Well I wish I had some of the outside but will attach what I have. I built my own garage (24 x 24) and still have a few items left to complete. Here's a few ideas I have to share:
1. I scored some 4' x 4' sections of bullet proof glass from a salvage yard - if you get mad and throw a wrench it won't even ding it and make it harder for people to brake in.
2. If a framed bldg. with a pitched roof then consider scissor trusses cause they give you a lot more ceiling height.
3. Metal roofs - these are great but make sure to tie yourself to something when installing them cause they get slick when temp goes below 75 degrees.
4. Put in lots of rebar and bolts to mount the walls in the foundation. I went over-board but it's cheap so why not.
5. Get various bids on the foundation work as it will vary quite a large amount and ask them all to spec what they think is code/appropriate and compare them.
6. I used a high-density exterior siding board vs. drywall on the interior and like it cause it doesn't require tape/texture and is more sturdy than drywall. Costs more for material but saves a lot of work in the long run and is a better product I screwed each piece in and can be easily removed if I want to change electrical or whatever.
7. Put in lots of outlets now while it's easy. Leave some extra power available up in the ceiling for ventilation fans or whatever later you may add.
8. Use 2 x 6 lumber and insulate well.
9. After you prepare your budget add 20% for all the little stuff you forgot.