Any clear residential or commercial roof surface can be a good water source:
Connecting a Rain Man water system to your roof can be the solution for:
Having a rain water catchment system as a main water source will improve the healthy of your:

A 2500 square foot can gather 1500 gallons from one inch of rain. In central Texas, that's 45,000 gallons in an average year!
Rain falls from the sky free of surface contaminants. Stored and filtered properly, it is the gold standard of pure drinking water.

This well-designed washbox shows how any leaves traveling with rainwater from the gutters are trapped and filtered out, so only clean water enters the storage tank.