In the states of northern Germany, we have a tradition to build houses with the roof made of water reed. (btw. this plant is called Reed, Schilf or Rohr in German)
Once, each house has had such a roof. Than, only the houses of poor people. Nowadays, the situation has changed: only the rich ones can afford such a roof. It lasts approximately 30 years and is a natural air-condition. It keeps the cold outside during winter and the heat outside during summer.
The houses in the image above, are vacation homes and quite new. But, there are still many privat houses around with this kind of roof, too.