I painted the inside of ours. I used a low VOC exterior latex paint (low VOC emits less toxic fumes, which is better for the chickens). I went with white, even though it will show dirt and such... It will also make it easier to see any mites in there. Planning to put down a cut of sheet latex flooring too, to make clean-up even easier. My babies will start spending time in their coop in about 2-3 weeks, so I am still putting on the finishing touches, but all I have read says that painted surfaces clean up better than plain wood. The paint also sealed a lot of small cracks and gaps, so i am sure that will help to keep the mite population down; and the paint really made the inside of the coop a lot brighter, which I am sure my girls will also appreciate. Good luck with your coop, whatever you decide!