C&C Stacked Cages?

My parents are probably letting me have the tiniest room in the house for the guinea pigs too live in (they've been living outside). I've been planning C&C cage designs, I want to have a 2x7, 2x6 and 2 2x4. But now we don't think they would all fit. Now we are thinking of making the cages stacked, 2x6 on top of the 2x7 and the 2 2x4 stacked on each other. How would I keep the, strong and easy to clean out and safe from my dogs. What's better for stacked, zip ties or connectors? Thank you
(Don't hate but I use too breed, that's why I need so many cages. But I don't breed any more and am against it ).