I think you might be thinking of ceder. The fumes can cause problems for chicks. Still, people use ceder bedding, to keep bugs away, with no problem. So you might have been thinking Ceder lumber use.
It's my understanding that treated lumber is okay with the exception of nest boxes and roosts, you should use untreated wood for those. Someone else may have a different (and more reliable) advise for you, but that's what I was told.
I would not use pressure treated lumber for roosts as mentioned. Roosts come into contact with relatively little moisture and there is no chance that it will rot out from under your birds. Preventing rotted wood is the sole purpose of using PT wood.
The birds spend a third or more of their lives with their feet gripping the roost. Why expose them for that much time to chemicals that are completely unnecessary for the use you propose?
Cedar has not been proven to be harmful. Pressure treated green lumber is treated using cyanide. A nasty substance. I do have it in my coop but not accessable to the chickens to play it safe although I do not believe it will be harmful after drying. The worry although small) would be fluid coming from the lumber or shavings. Just make sure you cut the lumber away from the chickens. Oh and use a dust mask yourself when using it and wash your hands afterward. Better safe then sorry.