There's no such thing as a cage "too big," essentially. Though, if given a ton of space, sometimes rats will only use parts of a cage (especially if there are different levels). But, you could always get the double CN, and if they don't use all of it, use the bottom part for storage. Plus, oftentimes people suffer from GGMR (gotta get more rats), so that extra room might be helpful to have in the future

Also, remember to look into adopting from a shelter/rescue, not purchasing animals from a pet store!
