Not to give you any ideas but I bought some equipment from a guy who made everything himself, frames included. About 3/4 of his boxes were osb and they obviously had bees in them for years and years. He painted the inside and outside. I didn't take any of these...
I have used osb (actually primarily osb siding) for lids and nuc boxes, but wouldn't use it on anything that you have exposed to the weather over winter.
I have made plenty of equipment out of scrap ply... It does warp, but...free is free