i agree with the idea of putting up a smaller insulated 'room/shop' inside the main building. as mentioned it's easily made bigger in the future if you make the walls up as seperate panels that bolt together.
neil.
I have one bay of my detached 3 car garage enclosed with 4 mil thick plastic sheeting on ceiling and walls. Not really insulated but small electric heaters can warm it up fairly well on cold days and the plastic keeps the heat in pretty good.