The Short Version
Do not get a cage smaller than a Petco Rat Manor. If the next bigger sized cage is only a little more than the one you're looking at, go larger. Your rats will thank you.
No hamster, guinea pig, rabbit cages or aquariums. Ferret cages should only be used with larger rats.
Don't waste your time and money on hardware cloth, 100% success stories are rare.
Use the cage calculator to determine the maximum number of rats the cage you are looking at can hold.
If you have the space, get a single Midwest Critter Nation. Even if you only have two rats, you'll be very glad you did. There is also a double unit for even more space. Check the Suggested Cages tab for inexpensive sites.