Hows this for a story idea?

It is about a thousand years into the future and society has fallen to pieces. The climate has changed to become much warmer, creating a rainforest-like environment. Many of the hardier creatures have mutated to become the top predators: roaches have become large, mantis-like creatures and rats have becme large, ferocious hunters. Other creatures include mice, which have only become larger. Cats have become longer, more streamlined, and much more agile. Dogs just much biggr. Birds either revert back to raptor-like reptiles or took to the skies as huge birds of prey. Humans remain the same, but the few tered gangs have become ruthless, sociopathic warmongering people and are constantly fighting among other gangs, or one-another. There remain several futuristic societies in large pyramid-like structures, very tered. few people live outside the cruel gangs, and those have tendencies towards a more humanlike emotions. The protagonist is one of them. He is about 15. When he was 8, a gang discovered his parents and older sister, and his parents were slaughtered before his eyes. His father had put up a fight though, and injured one of them. His sister had been taken away, and he knew little of what happened to her. He had been living alone in the ruins of a highrise, in the middle of an overgrown, enormous metropolis. using his wits, and the skills he learned from his parents to keep surviving. One day, he comes back to his camp after hunting, and finds a girl about his age taking his supplies. At first they are hostile towards each other, but when the protagonist realizes how feeble and injured she is, he stops.Having never talked to anyone else in many years, he does not know much how to talk to anyone. For a day they don't exchange a word, until finally she tells of how she was kidnaped by one of the gangs, but escaped. When they track her to his building they are both captured and forced to escape all over again, but out in the wild where not only are they being hunted by the gangs, but animals as well. I will introduce two more protagonists, and three main antagonists.