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?

I wouldn't use either, if solid wood (either close framing or ventilation and subfloor-type
planks) was an option. OSB doesn't take strain and moisture changes both, it'll sag.
Wood preservative painted-on should suffice, or PT. OSB will be less structural than
you want, plywood is pricey.

Heck, it's a shed; let the floorboards squeak.