Hey Dan,
The dual pane glass came from 8' sliding patio doors. I aquired 3 of these from 2 sets of doors (the 4th one was hazed over with the seal broken). I know the back panel I used for each frame was a true 4' wide and cut to length from a 4 x 8 sheet of plywood.
If I remember correctly I think the glass is 76 or 78" long and must be no less than 46" wide. These are very heavy, I needed to go 3/4" deep with the routered inset for a flush glass to frame fit before installing the aluminum frame, this included the glazing installation seal set under the glass.
The total exterior depth of the panels less the aluminum frame is 4". The sides are 2 x 4's on edge secured to the back panel with gavanized deck screws and construction adhesive. The flat plate absorber is sheet steel painted with flat black stove paint. This is secured to 1/2" rigid foam insulation (the good stuff with high temp ratings) with pure silicone caulk. The vent holes are 4" diameter.
As is normal with a first time project I did not work off of plans and have not drawn this yet, I plan to in the near future so as to be able to duplicate it. Thank you both for your interest in these solar hot air panels, they are not as exciting as the wind generator but they are extremely effective even way up here in NY. Dave B.