As I said to my DH, often, while building, IT'S A CHICKEN COOP!. It has to provide what they need, be secure, be cleanable without spending my whole day out there. I have windows, with the gray there is not huge shine or reflection with the semi gloss. Any shine that it has when newly painted is going to fade, rather quickly, from use, dust, dirt, droppings, cleanings, etc. Honestly, I like things to be attractive too, much nicer to look at, but in the long run functionality in a coop is going to be far more important and will be what drives you nuts if it's not. Almost no one will likely see the inside except the chickens and whomever does the cleaning and maintenance. I honestly can't imaging cleaning bare wood surfaces in my coop. I'd lose my mind. Sometimes I think that the inspiration for epoxy was chicken poop (cecal particularly). Flat paint would probably seal everything up also, but for cleaning and scrubbing, not sure it would stand up as well. Not to mention when a cut comb and a shaken head sends blood drops flying into every corner. Stuff happens. Do what you can live with and what works for you.