OSB swells too much when it gets rained on. You can't paint it
because the paint causes it to swell and peel.
MDF (medium density fiberboard) will work for boxes,
but you have to paint it first and it's VERY heavy.
I can't even lift a 4 X 8 sheet of 3/4" MDF by myself.
I'll stick with pine or when I can afford it, cypress