My garage is 24 deep to, but Id suggest going at least 26 or preferably 28 deep. With work bench, shelving, etc that 24 will seem very small in a hurry. If you consider heating the shop, use Wirsbo in slab tubing heated with a Gas water heater that also heats your hot water for your wash sink. Expensive but oh so nice in winter when you are on your back on the slab.
Also do a search in Bench section for 'garage' and you will find several very long posts with tons of ideas just like what you are looking for.
good luck, and build as big as you can afford.
69RS 350/255 LM1, Balanced, TRW forged pistons, .30 over, TH-350 auto.,
Dover White,Blue Vinyl top, F&R spoilers,pdb, close ratio ps,am/fm,3.08 Posi., A/C, fold down rear seat
My RS www.brainerd.net/~knudsen/69RS