Rats need to be kept in cages; it's a basic part of rat ownership. They can't be free-roamed full time. It would be very hard, maybe impossible, to make a free roam space safe for living full time. Cages keep our rats safe and protected from getting lost, chewing things that aren't safe for them, etc. Because rats are in their cages for most of their time, they need to meet all of their needs.
A good cage needs to:
And ideally should also have:
Rats have sensitive respiratory systems, so they need plenty of ventilation. However, too much draft can aggravate their systems, so placement of their cage near vents or open windows should be noted. The cage needs to be made out of metal or a strong enough plastic that won't be chewed through. Metal and plastic are both easy to clean and don't hold onto pee or ammonia. A good base is good for similar reasons. Rats need enough bedding to soak up ammonia. A lot of bedding is also good for enrichment. Rats are terrestrial, meaning they prefer digging and burrowing over climbing. They're decent climbers though, and climbing is good exercise. Platforms that are removable lets you add more into the cage. Platforms need to be solid and not wire for safety reasons.
Bad cages and characteristics include:
Tanks and tank toppers have low ventilation and contribute to respiratory infections. Tank toppers, as well as a lot of other cages, tend to be cheaply made with low structural integrity. An example of another cage that's unsturdy is the You & Me Rat Manor. It doesn't hold together well, especially without the levels (which need to be covered or removed, as they are made of wire). Exposed wire in the cage tends to collect bacteria and commonly causes bumblefoot. Material is also important when looking at cages. Wooden cages are very easily chewed through and also soak up pee. Wood is hard to clean, especially large wooden structures like cages. Another issue is tall cages. Rats prefer floor space to height, so having a very tall and skinny cage is a problem of its own. However, tall cages pose a fall risk, especially if you don't have things in your cage (like ropes or hammocks) that act as fall breakers. Rats aren't the best climbers and can get seriously injured from falls.