My garage is 28 x 28, 10’ 4” rafter height, lift sits about 7’ in from the door. No problem stacking Corvettes as long as I back the top one in to clear the garage door opener. It was just my dumb luck that it turned out like that - no Corvettes when it was built. I might have been able to go 32’ deep, but not sure it would have cleared set back requirements. 

I would build it to lift the largest vehicle you may ever think of owning, and push the lift as far in as you can. That way you still have most of the space for everyday living. Hope that helps. Dennis