Forgot to add the outsideI had the same thoughts about what to do to the walls. So being I always overdo everything (according to my wife) that I build I decided to sheet with 1/2 sanded sheathing and then cover with Commercial food grade 1/16 in. x 4 ft. x 8 ft. Plastic Panel. Resist bacteria, mold, and rot, instead of painting. I am not finished yet I have the plastic moldings that will go in the corners with sealant behind to prevent leakage into the walls or hiding spots for bugs. This 4x8 coop will cost an extra couple hundred dollars but I will never have to worry about the inside being unable to be kept clean.