The setting of a cramped, lightless apartment filled with five people indicates a conflict of interest from the very beginning of A Raisin in the Sun.
The family is forced, firstly, to share a set of circumstances and to deal with those circumstances. Each character deals with the limitations of the apartment differently as well as the limitations placed upon them by finances, racial discrimination, marital status, etc.
Each character sees the apartment in a negative light, which indicates the yearning of each character for change (material and spiritual change).
We can look at the shared apartment as being symbolically related to the money the family receives. The money will be shared too and there is not enough of it to do everything that each individual character wants to do. Finding a way to compromise and dealing with this particular limitation turns into one of the central conflicts of the play.