HOLY HOT HECK IN A HANDBASKET WHY DIDN'T I THINK OF THIS
That might actually be an awesome idea. You can find all KINDS of old campers & such, and if it doesn't have to be moved around much, you can find pretty much anything. It'd be like a tiny house.
I had a thread going about buying an antique school bus & setting up to live in that, but if you don't have to travel, a camper trailer is a much better choice--and the idea of a shed is perfect. Sheds are amazing.