[Imogen]

I'm not quite sure what you're trying to ask.

Are you saying this person who used their hamster cage as a cats litter tray is planning to re-use that same cage to rehome the hamster?

By all means, throw the cage away and get a 450 sq inch cage, hamsters should not live in a small cage and judging by how it's an old cage that was used as a litter tray (because it's small enough) that is definitely not ok to keep a hamster in.

Hamsters require a big environment and a substrate depth of 15-20cm to burrow and carry out natural behaviours.

As with that "litter tray" as well, do not use it since cats can carry germs and bad bacteria in their faeces that may even possibly kill a hamster. Things like feline influenza (cat flu) can't be passed on to hamsters since it's well, cat flu. But things like worms (tape worms) CAN be passed on to hamsters as well as other various diseases. And please take this seriously, I'm a former graduated college student who has an A level in Animal Management (care of animals) and studied all sorts of things from diseases down to biology of how their bodies work and genetics of breeding so please do NOT use that cage!

I recommend researching into basic hamster care and making sure they know how to look after a hamster properly before selling/giving to someone.