Well I have a female and a male right now and I think she may be pregnant. Mind these are pet store rats and I only bothered getting them since one of my BPs will now only take live, even after a month and a half of not eating so I could get her on f/t. Weird thing was she was fine on f/t and then one day stopped eating them and didnt eat for like 3 weeks so I got a buttload of mice and fed them off to her over a couple weeks, and since then I've been trying to get her back on f/t but she wont have any of it (she will strike if I move it rapidly across her field of view, but then she leaves them there. Kinda irritating, but she will take live no problem ~_~ This weekend I'm gunna pick up some more mice and feed her those until my rat gives birth and she can move on to rats. She's still too small to eat pet store sized "smalls."

But yeah I love your rack and it seems like an amazing idea for the future (I would probably only go with one or two tub tiers) and it will probably take up less floorspace than the big tub I have them in now.