Got them as chicks? So about 6 months old? What breed? What has your weather been like? It's been wet and cold here, mine like to sleep outside too, but it takes them a few days to adjust to these quick weather changes.
Deworming is a choice, depending on your own situation. Not always necessary, but worms can devastate a flock quickly.
Check his crop first thing in the morning, before he has a chance to eat. The crop should be empty/flat. Also look under his feathers, especially up under the wings, looking for bugs/mites/lice etc. Check his legs for scaly mites. Also take a good look at the hens. They could be better at hiding symptoms than he is.
If you can, try to watch him poop and see what it looks like. There are many different kinds of poops that are normal, but some poops can identify problems quickly. Take pics and post if you can.
Best of luck!