Do yourself a huge favor, and plan for a way to catch and drain the water in your new custom cage. I've used a plastic pan, they sell at Home Depot or Menards, meant for washing machines. It's square and has a hole you can knock out and attach a drainage tube. I attached a tube and sent the waste water to a bucket, so I could empty it once a week. Made it a lot easier. It's easier to plan it during the build than try to fix it later.
You could also look for the plastic pans they sell for dog crates or rabbit cages, they look like they would work, too.