I saw a documentary once about a group of indigenous peoples who literally built their islands, their homes, out of reeds. The Uru or Uros are indigenous to the area of Peru and Bolivia and live on islands in the shared Lake Titicaca. Currently, they live on approximately 120 man-made floating islands in the lake, and are continuously growing. The Uru use bundles of dried totora reeds to make reed boats (balsas), and to make the islands themselves. Smaller islands hold two or three family units while some of the larger islands hold up to ten families.
Over at Rolandomio Travel you can find a post about visiting these innovative people and seeing the floating islands for yourself! Go check it out!