My daughter had her rats in a huge Martin rat cage condo. It was 5ft high, 4 stories, 3-4 feet wide. The thing was huge. I still have the cage at my house. but no rats and no daughter. (she got married and moved out). Each story had hammocks, and various tunnels to play and sleep in. The bottom floor had the litter boxes, as all the rats did very well in using the boxes. She had 6 rats in there. All got along well. She was given a skinny rat, named Harry, who got along with eveyone else but got scratched more often than the others. As others have said, the bigger the cage the better.
We fed the lab blocks, along with the mixture that was on rats rule, fruits, veggies, and treats. A special treat was cheetos. They all loved cheetos.
Her room like Matt, was rat proofed and all roamed from cage to bed to room when she was home. She had ferrets at the time also. (She had 4 and they all lived in a huge ferret condo in another room.) We had to keep a very close I on the ferrets as they will hurt/kill the rats. They would also go after my
GP's. (just a waringing if you want ferrets along with rats and
GP's)
Anyway let us know what you decide.