I love the idea of collecting rain water and using it instead of city water or even well water, wasting electricity and wear and tear to run a pump.
However, so many systems are ONE 55-gallon drum. That's just NOT a lot of water compared to what nearly any roof can provide.
I help build a rain-water collection system at my parent's house. We started with one IBC container, and then eventually expanded it to three.
The containers are boxed in, both for strength, and to keep light out. The finished box is is the same style and color as the existing building, so it blends in well. It's a pretty good DIY system for over 800 gallons of water.
DIY 275 Gallon Rainwater Collection : Learning Experiences and Future Improvements.