My friend re-did her shed. She added better insulation, a better floor, a better window, a ceiling fan and upgraded the wiring to handle all the electricity of three or four sewers plus iron plus lighting. It's in the shady part of the yard so it only gets really hot in the really hot weather. I have sewed out there in 85 degree weather and with the ceiling fan and another desk fan, it was ok. She looked into putting heating out there, and the cost was more than she could do. But it's good for three seasons anyway. In the winter when we sew we sew at the kitchen table in her house, or she comes to my house. I think if you go the shed route you need to make sure the temperature swings are not too high and low or moisture may be a problem. Do you know anyone you can discuss your ideas with, like a contractor or builder?