A few years ago, I had a pair of rats in a rubbermaid cage with a wood-framed screened lid. They were fine in there for a few months. Then one day I came to check on them to find a hole chewed in the wall. The male was too big to fit through the hole, but the female and her babies were running around loose. It was a pain catching them. Just because they don't immediately chew through the cage doesn't mean that they won't eventually do it.