You can buy galvanised steel water butts. I don't know what their quality is like as I haven't been able to get one yet, but when I get a chance to install a water butt, it's what I plan to use.
Its quite easy to make rainwater harvesting tanks from so called ferrocement, which is basically chickenmesh plastered with a thin layer of cement/sand mixture.
As for the shingles: I guess you could settle out or filter any solids that get washed off the roof?
One thing that's important to be aware of is that some regions have laws that prohibit the collection of rainwater. So be sure to check the laws that apply to your region.
..... Okay I'll bite
Why on earth would they prohibit that?
OP's wildly misunderstanding. The idea behind such laws is that some asshole doesn't divert acres and acres of rainwater for his personal use. I think one guy, ever, has been prosecuted, and that's exactly what he was doing.
tl;dr: No one's coming for you after a rain barrel.
That's because you wouldnt be prosecuted unless it was a massive operation... you'd be fined by your local bylaw enforcement officer until you remove said rain barrel... thats not even counting the sorry saps who have to deal with HOAs. Happens ALL THE TIME. Maybe you are just lucky where you live.
OP’s wildly misunderstanding.
I'd say it's more just an overabundance of caution — rainwater collection laws aren't without precedent. Admittedly, given the context of OP's post, my comment doesn't warrant much concern.
I wouldn't collect from shingles. I routinely see bits of them in my downspouts when it rains.
Farm all the things!
Also see: