Question about rain collection and organic gardening?

Do the plastic rain barrels off-gas chemicals into the rain water that would pollute the soil and vegetables?

Are there alternatives to plastic rain collection barrels???

What type of roofing do you need to use for rain collection so that chemicals from the roofing materials do not get washed into the water, and into the soil and vegetables???

Any info would be great. I would like to try and turn our little urban home into an ‘urban homestead’ and become a bit more self-sufficient. Thanks.