I would go with 24' wide and go with 30' depth.
1 As I said before you will be able to fit a big bolt
in.
2 Have room to have a big bench in front of the truck
or car when working.
3 Room enough to use an engine hoist and keep the
truck or car inside the shop.
Jeffrey
I would go that big if I could. Zoning says no bigger than 600SF. That's 24 X 25.
I was looking at lifts. Most lifts need 11.5 feet from outside footplate to outside opposite footplate.
That will barely squeeze into one side if I go 24 X 24. I might need to go 23 deep X 26 wide. (598SF).