Another thing to consider is making the ceiling as high as you can, 12 feet is great if you can do it, since the electric 4-post lifts have become so affordable in recent years, and also will allow you to park two cars in the space of one...
I would also go for a 9' height on the garage door opening if you can. You never know if you'll want to get a boat or something in there someday...if even just to work on it...