I'll start by telling you I am a plumber Plantoid. So I use PVC pipes and fittings all the time. PVC has the advantage over other waste pipe that it can be 'solvent welded' together -the fitting and pipe melts in contact with the solvent and when the solvent evaporates (24hours) the joint is permanent. Problem with any unreinforced thermoplastic is it hates being subjected to continuous forces. So it bends, more so in hot weather, and stays set in that bend. More heat and more bend until it collapses. I fix loads of waste pipes that have collapsed over their length simply due to the weight of the water in them. It's not cheap either. A run made of it would simply blow away unless anchored. The only thing I have used it for is as a support frame for a small net over my veg. It also gets brittle over time with sunlight exposure, particularly when very cold, then just snaps. Black is the best colour to resist that, but then it expands 4 x more than white in heat. So I can't see it making a very durable coop, but it would be rather complicated fun sticking all the bits together. If you do go ahead invest in a 'pipe slice' from a plumbing shop. It will save you hours of sawing and cleaning the ends.
Hope this is helpful.