A good thesis statement would relate to one of the key thematic aspects of this play, which is dreams and their importance to the characters. It is very obvious from the early scenes in the play that each of the main characters has their own dream of how they can rise above the circumstances that threaten to keep them pressed down in society. Beneatha, for example, dreams of being a doctor, Walter of having her own business and Mama of having a house for all of them where they can thrive. The dream of Walter is something he refers to when talking proudly to Travis about his future life when he has achieved that dream:
You wouldn’t understand yet, son, but your daddy’s gonna make a transaction... a business transaction that’s going to change our lives... That’s how come one day when you ‘bout seventeen years old I’ll come home... I’ll pull the car up on the driveway... just a plain black Chrysler, I think, with white walls—no—black tires... the gardener will be clipping away at the hedges and he’ll say, “Good evening, Mr. Younger.” And I’ll say, “Hello, Jefferson, how are you this evening?”
It is clear from the details of this dream that Walter's dream is made up of a combination of the conversations he would have heard working as a chauffeur and also his own impression of the kind of houses such people live in and the cars they own. However, the quote does continue to talk about him having a better relationship with Ruth and Travis being able to study at any university, which indicates his dream is not entirely materialistic.
What happens during the course of the play, however, is that each character realises that the most important dream for them as a family is to own their own house, as it unites them as a family. Each one of them is therefore willing to put aside--temporarily perhaps--their own personal dream in order for them to pursue this dream. A good thesis statement would therefore be:
The characters in A Raisin in the Sun each pursue their own individual dream, but by the end put their individual dreams aside to pursue a collective dream that they recognise is vital for their unity and survival as a family.
This allows for an exploration of dreams whilst also ensuring that the one dream of having a house is focused on with sufficient importance.