Seems like everyone who has ratties gets the urge to construct larger and more elaborate homes for them. I've been bitten by the bug too. My plan is to put 2 large bookshelves (Flarke type from Ikea) back to back, attach hardware cloth and make doors for the shelf layers. It's a simple plan but there is a lot of advice about not using wood for the shelving as it soaks up urine and harbors mites and lice. I did find a polyvinyl spray that is supposed to be 'household chemical proof' so that should make things easier when it comes to cleanup time. Given that ammonia is a household chemical I'm hoping that urine won't soak through. Once the new cage is built and ready to go I'll post about how well (or how badly) the spray worked. Hopefully I'll have photo's of their new home too.