Mine is in my garage. I have one of those funky garages that has a little storage addition on the side. It is 11'6" x 10'6". It is all concrete block. I studded it out and turned it into a rather nice heated shop for woodturning. Then my machining bug hit me from years ago, so then I had to get a few metal working machines, and well, now I have a pretty packed shop. I have 2 wood lathes, wood bandsaw, metal bandsaw, Sieg SX3 CNC Mill, HF 8 x 12 lathe (manual so far), 8' workbench a few mobile table stands, dust collector, and shelves all around the ceiling.
I'm a little packed, but it's a very workable space and I have managed to pack 5 people in there all turning on wood lathes at the same time (woodturners get together) and we were comfortable. I did have to move a few machines out to the main garage tho for that one.