So in the shops, they have those hydraulic vehicle lifts that jack the things like 6' in the air so the mechanics can stand under them to do vehicle maintenance. It's not really the height that matters, but the fact that you have more maneuverability under the car. So I cut a 6' x 3.5' hole in the garage floor, and dug it 4' deep. I built cinder block walls on all 4 sides, and left the floor dirt to let any rain water drain away. Now, I drive the car over the hole, so that it straddles the 3.5' dimension, and typically, the car only covers part of the 6', so getting in and out is a snap.
I borrowed a friend's cement saw, and dug it out by hand. The whole thing took a day to build and about $100 of cinder blocks/rebar/morter. When I'm not using it, I usually leave the car parked over top of it to prevent accidents... It's amazing how much difference it makes in working under a car.
