Flame, I am no expert on duck boxes or the materials that they require, but I can say that regular ole' pine (whitewood) 1 by's hold up incredibly well for bluebird boxes and bird feeders. I typically, but not always, paint them white and put a solid weather proof roof on them. Something like a piece of barn tin or thick plastic sheeting can yield a lot of weather protection when used as a roof. Also, most plywoods, except the marine grades, degrade fast in the outdoors.
