IMHO, a seven foot ceiling isn't adequate for working on vehicles, especially trucks.
A friend of mines dad many years ago wanted to add a second story to their house. He decided that he already had a good roof, so he raised the house and added another level beneath. He didn't just dig out the basement but really did raise the entire house and framed another story under the old.
Raise the roof,raise the building or build a new garage if you have the room.
Another option would be to buy a large shop with a detached house.
John
