So, my husband caved in and is letting me convert our spare (unused and empty) bedroom into a Rat Room. We [might] be accepting my sister's now-empty double CN to combine with a second CN. While I've made a lot of toys/beds/etc. for my girls, I have no experience combining cages and have a few questions. 1. My primary concern: Are 2 Double CN cages together too much space for 3 rats, or is it a case of the more space, the better? 2. Are zip ties sturdy enough to hold two Double CN cages side-by-side, or is it advised to use metal ties? 3. Any recommendations for protecting the floor while the little beasts free-roam? We have laminate now. Previous free-roaming was always on vinyl or bathroom tile, so I never worried about it. 4. Adding extra shelves to a cage: What sort of materials do you recommend? I have coroplast I use for scatterguards; but feel it's too light to adequately support their weight and hyperactivity. 5. Any type of door-blocking gate/pen anyone recommends? If I can avoid it, I want to let the door stay open for ventilation even while I am in there (supervising) their free-roaming time. I do have a small animal playpen, but the gaps in the wire are a little too wide for the young ones (about 1"). Any help or suggestions are appreciated!