Thanks everyone! I love the idea of filling the kitchen with hay, I'm just worried it'll spill out the sides. Any experience with this?
The PVC is 4". They don't use it often but they are American guinea pigs so they seem to fit fine. The 5" scared them for some reason.
The cage is on a custom stand I built. It took several two by fours, 1/2 plywood, screws, and paint. It's 2' off the ground, which is perfect for storage to fit underneath, and is the exact size of a 4x4 plus the 1" or so added for the connectors. Then I put trim on the top edge to keep the cage from slipping around.