'Modern' ACQ or borate-treated wood is considerably safer than the green CCA stuff that was standard til, what, maybe 5-8 years ago. I would not personally use the CCA for roosts (actually would avoid any pressure treated for roosts) because they stand on 'em barefoot for like 12 hrs a day. I also would not allow any deteriorating pressure-treated wood where chickens could get at it, as they sometimes do peck at decaying wood.
Beyond that, though, since chickens do not peck/eat sound wood, any risks (e.g. 'something leaches into soil, is taken up by bugs or plants, eaten by chcikens') are purely theoretical and indirect, and if you do the math, incredibly miniscule. Of course it's up to each person to decide what they want to do about incredibly miniscule risks.
Two things to remember: 1) for ground contact wood (posts in ground, and anything resting on the ground or within a couple inches of it), if you don't use pressure-treated, whatcha gonna use instead. Untreated wood of most species will rot within a year or few years; even redwood or cedar don't last very long unless they are all (or mostly) heartwood, which is expensive. And 2) it is kinda stupid to use pressure-treated wood for things that are NOT ground-contact or otherwise damp/soggy; it's more expensive, heavier, splits and twists worse, requires more-expensive nails/screws/hardware unless you want things to rust through real fast, and even if there are no major concerns with chemicals leaching into the soil, the chemicals used in production of pressure-treated wood (even the modern stuff) are *not* friendly things at the level of "factory production of p/t wood" so it is probably best to minimize how much they need to be used.
JMHO, good luck, have fun,
Pat