Very hard to do by yourself. To grow a big healthy gorilla you need a rainforest between 9,000 and 12,000 ft. above sea-level. Lowland gorillas - rainforest up to about 8,000 ft.
http://www.ypte.org.uk/animal/gorilla/123
And an awful lot of bananas. I don't recommend. Try LR2! It is a lot easier.