We recently wrote an ezine article on the benefits of using discarded old car tires (UK  spelling tyres) to make a practical worm farm that costs virtually nothing to construct. See our article at   -  

 http://ezinearticles.com/?Stacked-Tire-Worm-Farm&id=2020501 .

There is more information on this highly economical ststem from Working-Worms at the following location -   

       http://working-worms.com/content/view/39/61/

Steve