I need a thesis that compares both LOTF and The Coral Island. Maybe something to do with isolation and civilization of man and society.
Because "The Coral Island" gives a similar scenario with radically different results, you could develop your thesis along the lines of comparing the two books' end results, then go on to discuss the reasons these results may have been reached in the two different situations. "The Coral Island" differs from "Lord of the Flies" in that the author determines from the outset that the evil that influences the boys is from outside sources, whereas Golding shows evil coming from within the boys themselves.
The article linked below gives some excellent information on both of these books (coral-island-revisited), and the other links, concerning how to write a research paper and comparing characters (think books in that instance), will help you in developing your thesis. Remember, though, that the only way to write an excellent thesis, and then an exceptional paper, is to thoroughly read both of the books you are comparing.