There are some great points already mentioned. I'll add my own.
My current shop is 25x75 and it works, but I have no room for additional personal projects. Beyond that, we want to continue to store our camper indoors to better keep it in great condition
I want to build a 40x100 at our next house. The garage doors will be set up so I can pull in with truck and trailer, drop off after a weekend of wheeling and deal with unloading later in the week. I'll set up the workbays so the trailer won't impede workflow.
Got to have a mezzanine area for storage and general cool factor.
A chain hoist on an I beam along the work area is imperative also. Plan to put the compressor outside to keep noise down inside.
It will have a clean room/office/parts room where things can kept cleaner than in the regulator shop environment. In the bathroom, a stand-up shower for obvious reasons
I want to fully plumb it with airlines outside each corner of the shop for trailers, campers, etc.
