I love cisterns, and grew up useing one.
I even have a rain barrel for the greenhouse.

Some things to point out:
Don't use asphalt shingles, or roofs treated with oil based preservatives or insecticides.
Use a flush box and a filter before the water goes into the cistern.

A plastic cistern kept above ground can be surounded with planks and black straps to look like a wood barrel, for appearance and protection from puncture.

Size a cistern for normal water usage for 1 year, with a 30% evaporation cushion, for your family.

Back in the 60's and 70's the Civil Defence suggested plastic sheeting be kept to cover a roof for a temporary emergency rain catch. (the idea being that the radioactive roof/fallout could not contaminate the collected water)

I'm a board member of a large Rural Water District. We have thousands of customers who only have rural water. Our district is very well prepared for the worst, but if we lose even 1 well from our system, or lose electric power for 2 days, we're down, maybe for months on some sections of the grid.
There is probably not a single municipal water system in the country that can go 3 days without power.