Something to think about with OSB. If you use it and it gets wet, it may start to separate.
If it does, your chickens will likely pick at it.
OSB, once wet, will harbor mold and/or mildew (rot) inside.
7/16" OSB @ Lowes is $7.97
15/32 Plywood is $15.57
Yes, plywood is about 2X the price, but how many sheets do you need? Even at 10 sheets, you're still only $80 difference for the whole project.
Build it once, or build it again later
Just a thought.
PS- Our coop is raised on 6x6 posts, so I hung 2x6 floor joists and used tongue-n-groove (TNG) plywood for the floor. It really sealed MUCH better. Though it was more, I only needed 3 sheets. We covered the floor (and a little up the walls) with sheet linoleum from the local outlet store to help prevent rot as we use the deep litter method.
- JC