Fragmites or water reed grows locally; thatch is a use for what is otherwise a nuisance invasive plant. Thatched roofs provide excellent insulation value and are completely waterproof due to the steep slope and the capillary action of the reeds which draw the water away from the interior.  Thatching is a highly skilled trade requiring years of apprenticeship and practice.  With proper care, a thatched roof can last longer than conventional roofing materials.