I would be careful about where the water is collected from before using it to water the chickens or any other animal. Roof water from a composite roof is not good for drinking, as it has been known to contaminate the runoff. Not good for drinking water, even for animals. Metal roofs are the best for that use.
I'm looking into just having a rain barrel in the chicken yard/run. Haven't looked into it any further but its an idea I want to research
