This was a fictional novel written at about an early middle school reading level.The book was set in an apartment building. The main character (a boy) had a pet rodent (I think it was a hamster or maybe a guinea pig?). The rodent kept escaping, and it is discovered that the rodent has joined a community of escaped rodents. The rodents are all intelligent and can communicate with the main character. The main character has to help the rodent community escape (or relocate?) to a different part of the apartment building.The cover of the book has a picture of a bunch of cardboard tubes that have been fashioned into an tunnel on the outside of the building, going from one apartment to another apartment a couple floors below. The tunnel is being used by the rodents for their escape.I found it in the children's section of my library either from 2007-2013.
A boy and his friends rescue their rodent pets from probable extermination and build a zoo where the animals can live safely.