This is a pic of the back of my home...
Each side is 24' deep by 48' wide, leaving room for 8 cars, 4 on each side with two double wide garage doors. To utilize the most space you can use a glu-lamb beam to span the 24' feet and then use a saddle bracket over the glu-lamb and attach seperate beams from the exterior walls to the saddle bracket. This elimates the need for an interior wall inside the garage, thus creating a fully useable 24' by 48' garage.
unfortunately, it is quite impossible to work on 4 automobiles all at once, at least in this application. Three is more realistic with one parked at an angle in the center.