I am in the process of building a 8x12 rat barn. I am using an existing shed that was in my backyard when I bought the house. It 2x4 construction with studs 16 inches on center. So far I have run power to the building, added a window, and put R13 in the walls and R38 in the ceiling. One of the concerns I had was ventilation so after some looking around I found a bathroom fan that is designed to go through the wall and vent outside. I know I will lose some heat in the winter and AC in the summer but it's only a 70 CFM fan so I'm hoping it won't be to bad. It is on a switch so I can only run it when I want to. All I have left to do is hang 1/2 inch drywall and install my light fixture. I plan to run a small window unit in the summer and a small space heater in the winter.