Try "Advantec" . It's a high quality OSB that is very weather resistant. Won"t swell up or warp, But it's heavy. It's used primarily as decking for floors of houses. I have it on a couple of hives.
Advantech... wax impregnated plywood.. Guranteed for 50 years, EVEN if submerged in water... I used it for my ROOF and floors when I built my new house in Maine.. that was... 20 years ago? When I built my new house here in Iowa they told me at the lumberyard they had never heard of it.. i just assumed it wasn't made anymore.. where did you find it?