If it was me building a new shop-- which I did last year, I would make it greater then 24' deep. 28' is the number I like best. The added depth gives me room to pull an engine and keep the car inside, with enough room to move the floor crane and still utilize the rebuild bench and work on the engine without having to shuffle things around. Also I would respectfully have you consider building the garage with a weight carrying I trush, made of wood overhead so you can use a chain hoist to suspend those bodies off the frame until the frame is ready to go back together. What a time safer this is when building a frame and then trying to fit the body mounts to it.
Just a couple of thoughts I had: that you may have not thought of... Chow!