Batch water heaters are simple to build, and its easy to get the impression that you can just throw anything together and it will work. But, batch heaters live in extreme temperatures (hot and cold), and you need to be a little careful about materials and construction:
Don't use plastic pipe:
Be careful about the glazing:
If using a used tank, be sure to pick the best one you can find.
Before spending effort on it, check it for leaks.
Clean it out well.
Sand and paint the outside with flat black paint. Most paints are OK, but some use high temperature barbeque paint.
Be Careful About Insulation:
The common polystyrene insulation board (this is the "pink", "blue" and "white" stuff) will not hold up to much above 130F, and the batch enclosure temperatures will exceed this, and melt the insulation.
An example: http://www.builditsolar.com/Experimental/pinkfoam.htm
Polyisocyanurate insulation board works well, and comes with an alum reflective surface already installed. Most lumber yards carry it, but may not know it by that name. It is usually light brown and is typically faced with aluminum foil.
I've not tested the Reflectix reflective insulation, but I'm a bit skeptical that it will have a long life inside a batch collector.
Be Careful About Freezing:
Some people who have freezing winters just disconnect and drain the batch heater for the winter. You just need to do this early enough in the season that you don't get pipe damage. Insulation on the pipes will help protect them from a cold snap, and will also reduce heat loss.
Some batch heaters are designed to be used all winter. They usually have some form of insulating cover that is closed when the sun is not on the collector. These batch heaters must have very good insulation on the pipes, or the pipe will freeze for sure.
If you take a little more time and care with the construction, and use the right materials, the batch heater will last for many years, and need little attention.