Most of the houses in Punjab have flat roots because it helps to generate heat in times of winter season and also helps to collect water at the time of rain. This allows them to have rain water harvesting which could help them in irrigation purposes.
Houses in Punjab  have flat roofs because they do rain water harvesting during rainy days and use them for their purposes all the year long .People in Punjab do roof water harvesting they have flat roofs where they collect water and store them in a tank where the pipe is connected to the roof .before collected they first drain the first showers of rain