Luckies mentioned Quality Cages. I love them. That's what I have for my ferrets. Here is there cage. It's 5 feet tall and 3 feet wide.

It has 3 basic sections sold separately that you stack all together. Each section has one main floor and a ramp to an enclosed balcony(which I love because my ferties always rolled off the balconies of my old Martin's when playing) What I also love is the ramps that lead to each section...you can leave them down for one big cage or attach them up to separate the sections...very useful if you don't want to take them out while cleaning...simply close them off in one section and clean the other or it's useful to separate if you need to quarentine one for awhile to watch behaviour.
Here's the website:
http://www.qualitycage.com/sacages.html
Of course, I'm describing their ferret cage. They have cages for ratties to, but none as big as the ferret quality cage.

Another awesome site for cages is Cages by Koch:
http://www.cagesbykoch.com/cages.html

These are also for ferrets. I'm not sure of the wire spacing for the floors, but they could probably be easily modified if you need smaller wire floor spacing for small ratty feet.

Good Luck. Hope you find what you're looking for.