What are some ways to hold a shelf in a rabbit cage up?

I'm thinking about building a rabbit cage out of wire grid cube shelving (can't remember the actual name) and I want to put shelves in the cage. I'm thinking about putting PVC piping underneath it as a support so the poor rabbit doesn't fall 2 feet while happily hopping around on the second level. Any other suggestions as to what I can use to make the shelf more stable for rabbits?