Finally I decided that this thing will never be done if I only use scrap materials. Recycling is a noble goal, but not if you never get to the finish line.
A quick trip to Lowe's and now I finished the roof (used leftover shingles from when the house was re-roofed after a hailstorm) and the floor. The floor is made from 1" thick white oak floating over a dirt bed. I was originally going to have a dirt floor with chicken wire to keep predators from digging in, but the wood was already there (my wife gave up on the bridge she was building for the little stream at the bottom of the pasture)
Tomorrow the birds should be moving in. The chicks are getting to be pullets now (hopefully no cockerels) and are almost too big for the cabinet-turned-brooder. The ducklings have been living in a big doghouse for a week now since they are definitely too big for the brooder.
Should post some pix if I can find my camera!