I've been asking Bill to built me a coldframe for a couple of years - every since I read Eliot Coleman's Four Season Harvest (*El's recommendation - see footnote for more about El). It took a while but it was well worth the wait. I should note that this is in our Chicago backyard.
The wall frames are constructed with scraps from a ReAdapted project from Black Locust which was sustainably harvested from Western IL near Galena. Black Locust is one of the hardest (and heaviest!) woods to work with. It is similar to Osage Orange and can last 100 years as fenceposts without treatment. The coldframe walls come apart with screws and wingnuts to allow it to be disassembled easily. The glass tops are made from old windows from my friend Mimi's house. She gave us the windows a couple of years ago and we left them outside in the weather on top of a sheet of plastic to allow the weather to do the majority of the paint removal (amazing what rain, sun and freeze thaw can do for you if you are patient). These are old windows and had years of paint (yes, lead paint). The paint flecked off onto the plastic so we were able to safely dispose of the paint chips. Bill then removed the glass from the frames, further removed any remaining paint, sealed them with an environmental soy-based sealer, reworked the frame, and then reinstalled the glass. He sanded down the low side of the window frame to allow water to run off. There are two eyehooks on the backside which, using the chain from the old windows (these are old double-hung windows), can hook on to the eyehooks to keep the frames propped open.