I salvage almost anything wood I find. Part of the fun in this hobby for me is spending as little as possible. I am also a contractor though and I know building materials pretty well. That said, I have not and would not use OSB for boxes. After letting it air out I do sometimes use it for tops and inner covers. I use solid wood for boxes but would use plywood for sides of boxes if I had solid ends on them. I also use plywood for tops, inner covers, and bottoms. I do not ever use MDF, it is junk and a waste of time and money even if it is free. If I use OSB or plywood I paint both sides.