Well, I finished assembling the basics of my greenhouse, and even set up a writing desk in here. In fact I'm writing this from the greenhouse right now, thanks to the miracle of wireless. When I came in this morning, it was 32 degrees inside, which was only two degrees warmer than outside. I've got some insulating to do, both with weatherstripping between the windows and frame, and some waterproof caulking on the outside. I discovered during the rainstorm other day that the greenhouse leaks horribly in one spot (the ceiling window/vent), which forced me to abandon work in the greenhouse.
Right now, within 1/2 hour of entering this morning, I turned on the little space heater and it's 55 degrees in here. I only plan on using the heater while I'm working in here, not to grow plants. But it's nice to know that this can be my winter writing studio, even if it feels like I'm working in a fish bowl.