Gatsby's house reflects his noveau riche state. He throws big parties, has a fancy pool, and owns more clothes than he could ever wear in his lifetime. This all comes from growing up poor and feeling inadequate in a society where money and materialism measure a person's worth. It is also telling that Gatsby's house, for all its size, is often empty, signalling how Gatsby's wealth cannot ever fulfill him.
The location of Gatsby's house says much too: he has it right across from the Buchanan house, which represents Daisy, the one thing he truly wants and that remains out of his reach no matter how much money he gets.
As for Nick's house, it is cheaper and flimsier than the other houses, and I think this reflects his alienation from both the East and West Egg, as well as the Valley of Ashes. He does not connect with the rich, and he doesn't connect much with the lower, working classes represented by the Wilsons either. He is the eternal outsider, flexible and able to mingle with all these classes, but never belonging to them and, as a result, never really coming into his own—until the end of the story, when he leaves town for good due to his disillusionment.
Nick's home is referred to as a bungalow particularly as "weather-beaten" and "cardboard". It also pales in comparison to the mansion next door and the others around him. I think this truly demonstrates Nick's character throughout the work because although he narrates, he is by far the least interesting of the three. His flaws are few and his action is less than exciting. He has no extrodinary affair, nor does he have a dicey marriage. He just exists to tell us this story. He seems pushed around by the other characters a bit, just as his house is beaten by the weather. Although his home is modest, which also matches him, it does seem to possess some great character. At least he has a Finn to serve him and details that make his home the feature of the story as it serves to give Daisy and Gatsby their reunion moment.
The Buchanan's place is gaudy and full of money. Using the idea of material wealth makes great sense as their homes match their characters, but beyond that, all of the Buchanans items are so superficial, just like they are. Tom cares about no one but himself. Daisy too, hides behind the material items they possess. Tom uses his home to help him start conversation. He even says, "I've got a nice place here." Normal people with at least an ounce of humility would let the onlooker make such a comment. This further shows Tom's character, he is not about to let anyone define him, he intends to do that himself, often to his own detriment.
When Nick first encounters the Buchanan's home, the windows are wide open and everything is painted as if it is floating, except when Tom is around, then doors and windows get closed and the environment becomes controlled. I think this is a reflection of the marriage between the Buchanans. Daisy is free-spirited and ready to have a good time, but is bound by the hulking brutality of her husband.