I have already build 4 racks like that. Only using the jumbo cat litter pans. I got the design off here. Just like yours only with the cat litter pans. I did pick up some black tubs like that. What size are they? Im looking to build something to hold all my weaned and small/med rats in. Until feeding day because right now Im still using tanks. And the tanks are getting old real fast. I know freedom breeder makes the rodent holder racks. But I dont have the cash to really spend on something like that. But that is what I was looking for, something big like that.