The floor is what we call particle board or press board. It's nothing more than wood chips glues and pressed together to make a desired size sheet. It is basically a sponge. You may be able to buy exterior sheet but I don't know. Let it get wet and it will come apart. Piece by piece but it will fall apart. Before it was used I would have painted it and water proofed it the best I could. Me personally, I would never use it for a floor. On a roof as an underlayment, or wall cover, but not on a floor. And you see why.
The water runoff needs to be directed in a way not to even get around the base of the coop. The floor is going to cease to exist. You ae going to walk in there one day and your foot is going to the ground. The other wood needs to be sealed to keep moisture out. Regardless what kind of wood it in it does need to be sealed. I use lindseed oil on all woods I intend to leave to outside exposure.
The water runoff needs to be directed in a way not to even get around the base of the coop. The floor is going to cease to exist. You ae going to walk in there one day and your foot is going to the ground. The other wood needs to be sealed to keep moisture out. Regardless what kind of wood it in it does need to be sealed. I use lindseed oil on all woods I intend to leave to outside exposure.