I built a 25x40 about, well it is still an ongoing project. I did 10' walls and a 6/12 roof. If I were to do it over again, I would go with 14' walls and have a loft in the rear part over my benches or a bonus room built into the trusses. That would clear a lot of my floor space against the walls that gets used for storage instead of work area. I would also run plumbing into the building. For electrical I have a 100 amp panel with 2 220v outlets and 35 110v outlets. Like Kurt, I have enough outlets but I would change locations of where they are. I would also advise deciding where your bench or main work area will be and splitting the outlets into several circuits at that location. Also, too much light is just about enough.
Garage journal is a great resource. That site combined with my limited funds which made my shop take 3 years to be built, roofed, wired and dry walled helped me avoid mistakes by planning, thinking and replanning before I completed each phase.