I'd expect cedar branches to be fine. They don't have the surface area shavings do to give off the fumes.
I'm building my coop and will use oak branches that are available due to our ice storm for roosts. I'll make mine easily removable so I can clean under them and treat them. I'll drive nails through them and drill a hole in the support to receive the nail, sort of like a peg. This will keep them from rolling.
Why would I want to treat them, you ask. A certain mite, I think red mite but I'm not sure of the name, hides under the roosts in cracks during the day and feeds off the chickens at night. One treatment is to coat the underside of the roost with motor oil to smother the mites. The bark on my oak branches is still too tight to easily come off. Once they dry enough, I'll take it off. Bark on cedar would be difficult to take off. I'd still use the cedar as I like the way it looks and they should be able to grasp it well with their feet, but I wanted to alert you to the risk in case you were unaware.
editted to add:
I see you only have a few posts, so are probably new. Welcome. And a suggestion. If you change your profile to show where you are, it helps in answering some questions. For example, a coop answer might be different for someone in Minneapolis than someone in El Paso. It took me a while to catch on to this, so I'm not criticizing, just suggesting.
