The houses in Cairo, Egypt (and, I think, some other parts of Middle East as well), are one of the most interesting things to notice. Majority of the houses are made of red bricks, and unplastered. You may also notice the steels hanging on the roof of these houses. Well, the explanation for all these is this: since a man in Egypt is allowed to have more than one wife, there is a chance of a man needing to add a new storey on top of the present house to accomodate the new wife (and subsequently her children with him). As such, these houses have uncomplete look.
Note: In Jordan, such houses are also found, and the roof of the houses can be used to distinguish between a Muslim and Christian family. The homes of Christian families will have furnished, complete roofs (without the hanging steels).