This is actually the first cage I got for my two rats. It's a ok starter cage for two rats but definitely too small for three. I ended up upgrading to the ferret kindom single which is pretty much the Australian equivalent of ferret nation. Its a great cage, so much more floor space though it was a pain in the butt to assemble.
a lot of people suggest the ferret nation http://www.amazon.com/Ferret-Nation-182-Double-Cage/dp/B000F4OX0E
I myself could not afford that but with sites like kijiji for canada and craigslist for USA i was able to get one quite similar to the ferret nation try checking out used ! just be sure theyre cleaned when you buy them
i just remembered something, if you do decide to get that cage you won't be able to take the wire floor out and use the plastic pan as the floor because of how the cage is made. Without the wire floor in, nothing is there to hold the front panel in and it can actually be pushed forward quite easily and enough for the rats to squirm their way out as I discovered while putting the cage together. heres what I mean:
You can still clip fleece to the wire bottom though
I think that is too small. I would say 80 x 50 x 80 (cm) at minimum fot two rats. But bigger is always better. My two boys live in Savic Suite Royal 95 (similar to critter nation double, I bought it used so it wasn't too expensive) and they love it and I love it too, so easy to decorate and clean and it looks so good! At firts I had a bird cage with custom shelves (cage calculator said it would be okay for 4 ratties) but that was way too small for active and playful young ratties. It wast okay when I had my older boys but I wouldn't use it anymore as a primary cage.
I would recommend checking out used cages as beccaneko suggested! That way you can possibly get a really nice cage and you dont have to pay a fortune.
Believe me, if I could find a used critter nation/ferret cage or similar I would take it. I'm trying to find a cage that will hold three rats, in Australia (so I don't have to pay too much for shipping), but everywhere I go it's either in America or brand new and costs $200+ AUD. I realise it's the price you pay for a really good cage, but...