Absolutely correct on the Extra Large. I've never known someone to have a garage that was too big. Known a bunch that were too small though. It doesn't cost that much more to make it large enough from the get-go.

Here in Alpine we built a 24 x 30 on a concrete slab with 2 x 6 studs, shiplap on the outside, insulated and with plywood interior. 18' insulated garage door on the 24' side. Because of the roof pitch, I also have a store room upstairs that is 12 by 30 with a 7' ceiling height. Stairs are at the back over part of the workbench. Metal roof. I've got room enough in it for the Porsche, Austin-Healey and 280SL and still have room to move around in it. By staggering the vehicles (Porsche in the middle and forward, Healey and 280SL back far enough to open doors all the way) I can work on any of them quite easily.

I contracted it myself. If my memory serves me correctly, the total cost was around $14k, nine years ago.

In Green Valley we also built a 24 x 30, but the door is on the 30' side, with the workbench on the inside front next to the door. No insulation needed there. Flat roof. Slump block construction.

I would have done much of the work on both of these structures, but I was still running my business and it was easier to earn the money there and pay someone else to build the garages. Added note: On hindsight, I could have made them a bit larger.......

Cheers,
Wes