Laws vary in different location regarding rainwater collection. Here in Utah, we are allowed 2 rain barrels per home. This means that you can’t “gang” multiple barrels. It is surprising how much water actually runs off your roof in a good storm. In an emergency you might be grateful to have the means of collecting rainwater. People usually use this kind of water for yard and garden, but if you filter and purify it you may also use it for culinary needs.
You will find a good video on how to build a rain barrel at the following link. https://www.youtube.com/watch?v=KOCsdxoAUxA I have actually done the same thing he does in this video. but added a tap instead of a straight pipe fitting. I have used a 55 gallon barrel with a spigot in my garden and I love having spigots on my emergency water storage barrels for easier water drainage.
As a side note – It is a good idea to have a small enough mesh on your netting that mosquitoes are not able to get into the rain barrel.