Last year I added on to my attached garage. It is now 26 deep and 30 wide. (was 26' deep by 18' wide.) Cost a small fortune to go attached, but went ahead with it. Last Dec, I replaced the engine in a '01 BMW 740iL (big car) and had enough room to have the cherry picker in ft of the car, door closed behind. (there's no work bench in front of that area yet. I'd go no less deep than 26' Also with work bench in place my chev ext cab shortbed is a snug enough fit, (I can open the tailgate with door closed and then just enough room to walk around the ft and back (sideways) Full 4 doors are really popular now and that'd be plenty tight. I have an 18' door with 6' on each side. That works out well, just wish I had more room property wise to go wider. Another 10-12' for a 3 car with room on the side would've been the real ticket, but not possible. 9' ceilings are nice too, can get shelving up high and out of the way. It really is sweet to have extra space to the sides for sleds, mower, bench, etc. You see tons of newer houses with 16' door and maybe 1foot to each side of the door, seems like such a waste of garage to me, but it all costs $$$$ and some dont do anything in garage other than park small cars so each to his own.
By the way, its not fully finished yet and I'm entirely certain that I've outgrown it already, still shuttling off season stuff to Dads shed to free up my space--something I was really hoping to get away from! Guess its time to start saving up for the detached pole shed now?!