When we bought our house it had a 10x12 storage room attached to a carport on the property. I mooched several 7x7 slabs of 3" foam from old hot tub covers from a guy who makes replacement covers. He was glad to get rid of the stuff. I tightly insulated the shop with the foam (yeah, I know it can burn, and when it does it makes fumes that will kill you, so please don't lecture me). I put the foam over the ceiling with 6" of fiberglas over that.

It rarely gets below zero in north Texas but we get plenty of below freezing days. Most of the time a 100 watt light bulb will keep it comfortable, but when it really gets down there a little electric baseboard heater on the lowest setting works fine.

At leasts this is the story I tell my wife to justify the $1500 I spent fixing up the shop.

Jim