I have no idea what your goals are, what your coop looks like, or how you plan to manage them. For some people there could be legitimate reasons why they paint the inside of the coop or at least parts of it. Personally I did not paint the inside of mine. The way my coop is built and the way I manage them, I did not consider it necessary. It’s pretty much a personal decision. People normally care about this a whole lot more than the chickens do.
I painted the inside of mine white. It helps reflect available sunlight and really brightens up the coop's interior. Makes it easier to see things that should not be in there, on the walls and ceiling. You don't have to, but it's a positive thing to do.
I didn't see a need to, but this is my first time with chickens so I didn't want to overlook something. I thought maybe it might make cleaning easier or protect the wood?
Coop is very similar to the purina one but I changed some elements of it. I was planning on using the deep litter method. I made one whole side of it so it opens for clean outs. The outside is painted barn red with white trim.
I thought I read something in the city laws about the inside being painted or white washed but now I don't...maybe I was imagining that.
I know the chickens won't care and I'd just as soon not because it will be tedious but if there is some advantage to it, now is the time to suck it up and do it, know what I mean?
There are different versions of the deep litter method. In the true dlm, the litter is kept moist enough that the bugs can decompose the litter and poop. Any wood in contact with that will rot. My coop floor is dirt. Jack used wood and he painted his with a specific preservative. But both Jack and I don't use the damp method. We keep ours extremely dry so the stuff doesn't decompose while in there. It does absorb moisture from the poop very well so we can go a long time in between cleanings but that stuff still needs to be composted when we take it out. It's probably a good idea to paint any wood that is going to be in contact with the deep litter, even if you try to keep it dry.
I had planned on using shavings. When I built the coop, I designed it to allow for the deeper litter. Hopefully it works out I guess. Their brooder has about 3 inches of bedding in about 12 sq feet of space with 15 four week olds and while there is a bit of an odor to it if I stick my head right in there, i don't smell it unless I really try. In a week they're going in the coop and run so they'll have lots more space. 2-3 weeks after that I will decide who is going and who is staying for the girls and get ready to process the boys since I can't keep them much past 8 weeks. In the end I will be left with 4-6 birds. The bedding will also be getting progressively deeper. So deeper litter with far fewer birds (and right now all their poop is going in the brooder, wen they go in the run they'll be pooping outside some too) so that should be okay. I hope. I guess we'll find out.