I had a "system" in my Pittsburgh house. I put that in quotes because it was pretty terrible, so maybe you can learn from my failures.
I had four blue barrels, one at each corner/downspout of the house. I just cut the downspouts and used some of the flexible stuff like Rons posted to make an elbow into the barrels. I cut a hole in the lid and epoxied on some aluminum window screen to catch the leaves and debris. I installed a hose bib about 6" from the bottom and attached a soaker hose to it which I buried in the flower beds. I figured I could open the valves overnight if we had a dry spell.
First problem was that the water and debris (leaves, twigs, etc) had enough force that they punched some holes in the screens. The barrel quickly got lots of leaves, pine needles, and grit from the shingles. If I didn't clean them out regularly, the debris got pushed into the soaker hoses or just clogged the hose bib. The frustrating part was that cleaning them meant disconnecting the hose, opening the valve to drain the water so I could handle them, and the debris often clogged the spiggot, which means I either left it for days to slowly drip out, or had to get a bucket to bail out the water.
Since it was Pittsburgh, I had to winterize them by draining the water and covering them. I had plenty of busted hose bibs and cracked soaker hoses if I waited or didn't have time for the maintenance.
I also had a "hay infusion" problem. If you never did a hay infusion in science class, it smells like rotting flesh. The combination of decaying leaves, bird droppings that got washed off the roof, worms and bugs that fell in, and the existence of some hot summer days meant that the barrels started to cook up a concoction that made you gag when you walked outside.
I think what I'm saying is that I failed big time, so maybe don't do it my way. I also wouldn't worry about food safe barrels. Rain water isn't food-safe, and neither is your roof or the squirrel poop that might be on the roof, so the barrel's composition likely doesn't have much to do with how clean the water is. Of course, you might want to transmission fluid barrels or glyphosate barrels for obvious reasons, but it doesn't really matter if it had tomato paste or linseed oil before you re-purposed it. The water source (the roof) will make it non-food-safe after the first rain anyway.