How would I craft a thesis statement about how Fitzgerald uses clothes to tell readers about characters and/or themes?

Throughout F. Scott Fitzgerald’s The Great Gatsby, Fitzgerald uses clothes to demonstrate characters’ socioeconomic status. This is especially true in relation to the titular character of the novel, Jay Gatsby. Gatsby’s clothes are needlessly ostentatious in an effort to attract Daisy’s attention, but his vibrant suits merely confirm his status as a member of the nouveau riche, or the “new rich.” Tom and Daisy Buchanan’s clothes are more subdued and subtle in comparison with Gatsby’s gaudy outfits that denote that even though he has a substantial sum of money, there is still a gap between Gatsby’s status as new money and Tom and Daisy’s comfortable designation as old money. Tom points out Gatsby’s ostentatious style during a tense lunch:

“'I said I'd been making a small investigation of his past.'

'And you found he was an Oxford man,' said Jordan helpfully.

'An Oxford man!' He was incredulous. 'Like hell he is he wears a pink suit.... Oxford, New Mexico... or something like that'” (109).

In this passage, Tom acknowledges that he considers Gatsby beneath him, and explicitly mentions his pink suit. If you were to construct a thesis statement concerning Fitzgerald’s treatment of clothes, I would suggest examining Gatsby’s garish clothing and comparing it to Tom and Daisy. I think that Fitzgerald's use of Gatsby's pink suit could be a very useful component to your analysis.