Why do you need a cage for a fresh water crocodile? You are not allowed to keep them as pets. If it is for a zoo, the fresh water crocodile needs a fairly large cage. It should be impossible for the croc to get out, as you do not want people to get hurt. There should be enough space to lie in the sun, as well as enough shade. And there should be a pond for the croc to swim in. But again, crocodiles should not be held as pets.