+2 on the deck screws. Safer than a hammer/nails and you can change your mind or fix a miscalculation. I just built my coop this weekend and I used 2x4 center on 16" for insulation purposes. OSB for the sides. Treated ply for the base. I will be painting my OSB to protect it
I have a post with some picts here if you want to see the progress.

I have a post with some picts here if you want to see the progress.