Saw one recently that was homemade but was effective and cheap to make. It consisted of a 40 gallon blue plastic barrel mounted on breeze blocks (it was about 3 feet off the ground). The barrel had a wooden cover with a hole in it to accept the downspout and there was chicken wire over the hole to keep out leaves etc. It had a tap low down with a 20' hose attached and it is used for watering flowers, I'd say you would get the same flow out of it as a watering can.It is very important to make sure that it is covered if you have children around because if a young one goes in to it head first they can't get out.
You could also make one from an old attic cistern tank ( probably pick one up in a scrapyard for peanuts) mount it say about 4 feet off the ground on a 2x4/6 framework and stick a tap on it.
I know a lad who is going to use a new 1000L plastic oil tank as a rainwater collection system for his house and use that to water for the garden ,washing the car etc so that is another idea.
Good luck.