Roll out the barrel (for rain, that is)

My rain barrels are simple.  I saved them from possibly living a life as garbage cans for greasy rags and broken parts.  They were liquid fertilizer barrels in their previous life.  Having them live out their useful days in a dusty garage seemed too cruel.  Someone had even suggested hauling them to a landfill!  It still makes me shudder.
The first barrel was my most eager attempt at capturing the water from my garage roof.  There is a spigot at the bottom.  I savaged an old brass faucet from a junk box, and not only does it work, it doesn't leak.  They don't make them like they used too... A nut and washer hold it to the inside, and on the outside, it functions just like any other faucet.  A little elevation off the ground and I was in business!

The second barrel is my quick and dirty model.  Like the first barrel I cut out the top to capture the water. This time I cut the hole as close to the edge as possible so I could use this one for filling my watering cans quickly and easily. 

The first one I had left a lip for fastening screen to the top for keeping out mosquitoes.  The second one has two layers of screen. The top one keeps out the bugs. The stiffer bottom piece of hardware cloth provides support to the finer screen and keeps out the critters.  I found out the hard way that chipmunks would be stupid enough to climb the barrel and fall in.  Not a pretty sight.  I figured I better do something stronger. The sharp edges also keeps out the neighborhood kids, which is good, as I do like most of them.  Mosquito dunks (a.k.a. Bt cake) can be floated in the barrel to also keep mosquitoes at bay and is not harmful for you or your plants.
Barrel two sits at ground level and is fed by barrel one as it overflows through the garden hose coming out as close to the top as I could get it.  I could fill both faster by having them on the opposite sides of the garage, each being filled by their own downspout.  Spouse number one is not fond of the blue barrels.  To keep peace in the house, I keep the barrels out of sight as far as possible.  They reside with the compost bin on the far side of the yard and all is well.  We don't have neighbors on that side so everyone is happy.

I am very fortunate, in rain barrel terms, to have a multi-level yard.  The barrels sit at the high side and gravity feeds the water down hill to most of my gardens.  A gardener could not ask for a better set up.  If I want to use a hose in the veggie garden, I attach it right to the rain barrel spigot and run it down hill.  The flow is just right for watering.  I can also use a pail to transfer water from barrel two to barrel one and use both barrels through the hose on barrel one.

I added a second feature to barrel two last year.  In previous years the water just over flowed the top after the barrel had filled.  Last year I took a short piece of hose with a male end that I salvaged from the bad hose pile and added an over-flow to the second barrel.  The male end is on the ground side and I was able to put a piece of soaker hose on that and transfer water to the planting area behind my garage.  It's not a perfect water transfer system, but it is better than the over-flow method.  
I put the barrels up yesterday as they are calling for a rainy weekend.  It is a good idea to keep some weight in the barrels to keep them from blowing over in a strong wind.  I put a couple gallons of water in the bottom of my empty barrels which is more than enough weight to keep them steady if we should have wind with our rain.
It is possible to go and purchase a rain barrel and be in business with the first good rain fall.  It is good to have a few tools at your disposal to shorten the downspout to barrel height.   If you construct your own from found materials, a saber saw or saws-all is helpful in cutting through the heavy plastic sides.  Larger drill bits are needed for spigot and hose over-flows.  Ask around the neighborhood if you don't have them yourself.  If you aren't good with tools, barter future veggies and flowers for the help in constructing the barrel.  Most people won't turn down homemade cookies as payment. It also helps your neighbors understand why you have that hideous thing sitting in your yard (can you believe that some people would think this???).  
You should also do a quick internet search to make sure your community doesn't have regulations or permit requirements first.  If you live in a newer subdivision, you might also have signed a covenant which will prohibit you from doing anything sensible in your own yard.  It may take some education to get changes there.
Good luck on your quest for rain water storage in your own yard.  The water has no chlorine or fluoride treatments which your plants don't like any way.  The sky is the limit on what you can accomplish!