On Thursday, March 22, 2018 at 7:04:04 AM UTC-7, Gramps' shop wrote:
I am putting up a kit shed on a 2x6 PT framed platform. The kit includes a plastic floor. Can I cover the platform with OSB or do I need pressure treated ply?

If it'll get some moisture, and if there's a wood floor over plastic, the wood
won't dry well. So, I'd consider polymer deck material instead of wood for
the floor. OSB is not much good when it gets cycles of moisture, and
plywood isn't a good wear surface, though paint can help.

The wood won't last long, though, if it gets wet and has paint and plastic
on its surfaces.