For $800 more, it's a no brainer....go bigger assuming you have room.
Other things to consider....
- Make the garage doors the same. I don't see a problem with 9' doors as long as you space them apart sufficiently so you don't bang your doors. If you aren't comfortable with that, do 10' doors so the aesthetically it looks right from the outside.
- Minimum 9' ceiling. Had a 10' ceiling in my last house and loved it. If you are considering a lift of any kind, I would try to swing a 12' depending on costs, etc. A nice perk here is you might be able to do a loft area with storage potential over some of the area.
- Run a big enough electric service and set a big panel for 2-3x what you plan now. Outlets need to be placed everywhere, much more frequently than "code" says. Also, think about things like a welder or lift that requires higher service amps.
- Plumbing....with a detached garage, you need a restroom in there and place to wash your hands at a minimum. Depending how crazy you get, a shower might be in order. Also, I'd consider a wash sink in the garage. You won't use it every day, but very nice to have.
- Lighting. You could spend a career doing that. As far as the building structure goes, have you considered using windows in the garage door? Or possibly skylights in the roof?
- If you do a lift, plan on for reinforced/thickened concrete slabs in those area. Also you don't want saw cuts where the legs will be placed.
