Well now that I am retired I want to spend some time in the shop, It is the lower level of a split. Takes up about 2/3 of it. It is basically a 2 car garage that is also 2 cars deep. In other words 2 side by side and room for two more in front of them. The back half sits on past the end of the house. It has cinder block up about 4 feet and above that is stud construction. The studded walls are insulated and sheetrocked. The ceiling is insulated but not sheetrocked.
So I took one of the doors and built a minimal false wall and installed it outside the garage door. Covered it with 4 mil poly for glazing. When the sun shines I open the door and let the sun shine in. This morning it was in the high 20's outside and the shop was 43. By sunset it was 54 in the shop and I had spent all day in it with no jacket. It never got over 33 outside all day.
I will add some pictures in a day or two but as it stands now it sure won't win any beauty contests. I think if I would insulate the cinder blocks and also do the second door I could work on most winter days.
The idea came from here but as I say this is just an experiment, and so far the dollars invested has been zero, so at this time it looks nothing like that. My doors face about 5 degrees east of south which is why I chose this option.