The cage she posted above is a good size for 2-3 girls. I've even housed 3 boys in it before. That said, it is not super sturdy... I had to reinforce the corners of mine with zip ties and used tiny binder clips to secure the doors (the doors just push closed and a very determined / strong rat might be able to push it open). Also, it has a plastic try which could be chewed if your girls are chewers. I ended up taking out the plastic shelves as they got urine on them all the time and were hard to remove to clean. Instead I hung several hammocks (you can fit like 4-5 if you use corners ones too) and they enjoyed that layout.
If your girls are smaller, the Petco Rat Manor can work. It is all metal and sturdier than the cage above, but it is a PITA to clean. I took out all the small levels (the wire gets coated with urine and they are very hard to wipe down). It held up well for over a year. If I end up uwing it again, I will likely try to remove the center floor and just fill it with hammocks.
Both of these cages are hard to put big things in, You would need to lift off the base to put in a wheel or anything else large. Some of the medium / larger martins cages would work well (just look for ones with dimensions as larger or larger than the kaytee cage above). They can be expensive though and you'd need to pay to powder coat it.
