We recently completed our newest rainwater cistern. It cost about $1,600 to make, and took us about a week. It holds 6,000 gallons of potable water, and can be made by just about anyone.
We start by leveling a site and making a ring of bricks. the bricks serve as a foundation for the metal walls of the cistern. Then, we lay out the metal in a cylinder, bolting it together. Once the walls are in place, we cut out holes for inlets and overflows.
The roof sits on a ledge of angle iron inside the walls. It consists of a PVC frame, covered by billboard vinyl, and then that is covered with a thin cap of acrylic concrete.
It is pretty easy to do, and gives you a cheap storage space for a lot of water. If you conserve water, this storage tank could last your family a very long time.
For more detailed instructions, please visit:http://www.velacreations.com/water/water-sources/item/313-cistern-howto.html