I want to get a big cat need help?

That's just selfish. Why would you get a cub, raise it and then once it gets older, get rid of it? A zoo is totally different environment than a house/pen, and after awhile of living in a house it could become stressful to the animal to move to a completely new environment/habitat. And if you're not in it for the long run, what would be the point of getting a wild animal? Would you be willing to give the animal live prey so it could meet it's exercise needs and eat? And would your parents be willing to build a LARGE cage in the backyard so the animal won't get out and possibly attack smaller animals and children? If the animal was to escape and harm somebody or a house animal, there's a large chance you could be sued. What are you going to do if one day the animal decides to play, and ends up severely harming you with it's nails or claws. Tigers can be up to 660lbs, what would you do if it pounced on you. These large breed animals were not bred to be house cats, and deserve to live in their natural habitat.