I’m only 2 years into chicken-ing, but I was told that once they’re feathered out, they’ll generate and maintain enough heat to be comfortable in moderate temps.
I put my babies out not too long ago, and was shocked to near heart-attack level, when I looked up at their ceiling, and saw a massive, 6’ plus snake!! Thank goodness I decided to put hardware cloth across the ceiling!
So, the only worry I would have is not having 1/4 “ or slightly larger, galvanized hardware cloth on the ceiling (if there’s any way anything can crawl into that space,) and on the floor, walls and covering all holes. You can have a skirt of HW cloth around your coop, but I’ve had things dig under that skirt and could have, with average effort, made it in with the chicks. I do live in southern Louisiana, so things slither, crawl and jump their way wherever they physically can! Kinda gross..lol.