I've heard quite a few people having problems using the concrete mixing tubs, the rats can chew through them and escape. Nothing worse than having rats running around the house LOL. I decided to go with a professional ARS rack system, it's expensive but its designed to contain rats, and the resell value is really high so I can recoup my cost if I ever need to. But if I were to make my own I'd buy the tubs from ARS and build the rest. They are really heavy duty tubs and proven to contain rats so that they can't chew out and escape.
http://arscaging.com/ars5032.html