Why do houses in hills have slanting roofs?

The reason for having  slanting roofs in the Hilly regions is, these regions experience severe rainfall all over the year. In order to allow the rainwater flow away, the roofs are slant. Otherwise, the roof collapses.

The weather conditions appear to be stronger on hills, rain, sunshine and even strong winds tend to have a greater impact on the house, so normaly the houses have slanting roofs to withstand these adverse conditions ..