Cedar is used on a lot of animal pens and outside shelters becuase it repels insects. I do think i read some where that cedar can be toxic to chickens if ingested (don't quote me on that) but i would believe unless your girls like pecking at the wood it's self,or there are a lot of frayed edges that might peck at they wont be able to get enough to do any harm. My girls are currently in 2 of those premade cedar coop and run setups and i haven't see any issues other the they want to free range like they did before we moved. Honestly the premade setups are very small in general, and I've found a few issues with them like the height of the roosts compared to the nests. But for a temporary sulotion is fine for us. I think everyone just has a preference, the hens however just want to feel safe.