Mr. Bud, Saw this earlier but had to chew on it for a bit.
I think if'n it were my project I would use 1/4" ply, 2 pieces about 16 inches long and 10" wide, and use a 16" 2x2 for a center beam. Just attach one panel to connecting sides of the 2xx4 and ya got a good frame that will last ya, and is about at the proper angle. Since I haven't tried this yet, if the "wings" are at too acute an angle you could easily place washers between the 1/4 ply piece and the 2x2 and run your screws through them, increasing the span of the reflector...(screws will make it "storable" of you ever need to place it in a drawer or out of the way) Should be lightweight enough not to require add'l support for the "wings".
Cover the wings and bottom frame with Mylar (I would try the diamond shape stuff as an experiment, but would likely go with the standard mylar (based on the tests results I've seen on-line.) Watch the angle though, as you want that light on your plants and not spreading too far.
Couple small eye-bolts on each end of the top to suspend it from, mount your CFL array to the center beam and you are all set.
Best I can come up with in a few hours. Working with reflector designs is a part of growing I'm interested in getting into as I learn more...using less wattage and getting more of the right colored lumens in the right spot is always good...
Dizzy