Good points. I'm still on the fence with the idea and it's great to get another opinion, thanks.Looks like a lot of weight to support, plus it'll be even noisier up there than on the floor since it can get everything to resonate. It'll also make the compressor run hotter and the air warmer (and wetter) in the summer.
If you have room, a little compressor shed attached to the exterior of the shop would be my choice.