Here is what I did last week
remember that 10sf of roof with an inch of rain will almost fill a 55 gallon barrel, that is why I currently have 8 barrels just for my garage roof and play to hook up 4 more, I'm not sure how I'm going to handle the flood of water from the house roof.
My barrels are steel and had Molasses in them from a cookie factory, feed stores might also do the same kind of thing, any sort of feed, food or supplement place is going to empty barrels, Mine were $5 each for a single barrel or $2 each if I bought 50 of them... it took me 12 hours to git rid of the extras after sending out a few emails to friends.