I'm thinking about adding a rain collector to use in my garden but I have some concerns about construction materials.
One concern is that I'm not a huge fan of using a plastic container to store water. The idea of water sitting in a plastic barrel that could be exposed to heat from direct sunlight doesn't fill me with excitement. I was wondering what other materials or containers I could use that might be better for storing rain water. One idea I had was to modify a metal keg to collect water. They would be smaller but I could use multiple if I wanted.
The other concern I have is about roofing materials. Is it safe to use water collected from a roof with shingles in a garden for vegetables? I'm wondering if there might be any run off from the materials used for roofing.
To my knowledge, agricultural plastic water totes (275gal or so) are uv treated and so degrade less quickly, but there are also cisterns and containers made from metal or cement that you could look into.
Asphalt shingles will release visible solids with rain events and can leach some of the compounds they were made from. Here is a link with some information you may find useful. It's tough to give a yes or no answer without knowing more specifics about your roof, but knowing the materials and age can help you figure out what your options are.