In terms of working on the firebird only, you could probably get by with 24' depth. I like the xtra depth because my 17' I/O fits with the lower unit extended plus the trailer hitch. Whenever I put my 'birds in the garage, there is tons of xtra room compared to when out Durango, boat, bobcat, and Grand Prix are all in the garage. I like the 10' bay widths, but not a lot of room to have two cars with the doors open at the same time. I use mine more for storage than working on. When I am working, I ususally use two bays at a time, which kicks something else outside.

Hence the need for another garage. (or at least that's what I tell my better half.)