Some possible thesis statements below:
1. Although Jay Gatsby lived his life loving Daisy, she did not even attend his funeral.
2. Although the night life was all glitter and glamor at West Egg, when the lights went out, money could not buy Jay Gatsby happiness.
3. Although Jay Gatsby was living the American Dream, he died in an unhappy state of mind.
4. The Great Gatsby is a classic novel in which money is the center of many characters' lives; however, that money could not buy happiness.
5. All the money in the world would not make Jay Gatsby happy for he lived to love Daisy Buchanan and died without her love.
6. The Great Gatsby is filled with many characters who live hopeless, lonely lives, even though they have all the money one could want.
7. Although Jay Gatsby acquired all the money he needed, he never reached his goal in having Daisy as his own.
8. Jay Gatsby lived in a dream world and died dreaming he could have daisy Buchanan, but in reality, Daisy would never have belonged to Gatsby.
9. The Great Gatsby is a tragic tale about a man who lost his life over a woman who did not even attend his funeral.
The above will serve you well when writing, but I think the more pertinent question is what type of prompt are you being asked to write on? Thesis statements can be very generic is the teacher or professor does not give you a clear topic on which to write. Furthermore, you run the risk of losing focus in your paper without a clear question and thesis.
Perhaps these two will help, as well as the others posted in previous responses. Just keep in mind the focus of the paper.
1. Gatsby was ultimately killed, not by a contrived, ominous chain of events, but rather, as Nick indicates, by what preyed on him: those who used, rather than appreciated, him.
2. Although Nick purports that he has reserved all judgment with regard to his summer in West Egg, however, myriad occasions reveal a deeper-seated bias against the characters in The Great Gatsby.