They can get the occasional smudge of poo on the roost, if they happen to have some on their feet. I don't usually get a lot of poo on the roost, but over time it doesn't look like it just came from the lumber yard. They get smudges of mud on it in rainy weather, too, at times. I usually run a sharp scraper over it, whenever it needs it. I like to keep a scraper hanging on a nail on the coop wall.
I also gently round the edges of 2x4s that I use for roosts.
I would use a wider, branch, too. If you ever have a mite problem, make sure you treat the bark thoroughly, since it has a lot of crevices that mites can hide in. It doesn't mean you shouldn't use a branch, just be aware of that.