Thatch is a natural product of reed, grass or heathers, when properly cut, dried, and thatched forms a waterproof roof. It is a naturally weather-resistant material and when properly maintained does not absorb a lot of water.
Thatch is also a natural insulator, and the air pockets within a straw thatch roof insulate the building in both warm and cold weather. A thatched roof will ensure that a building will be cool in summer and warm in winter.
Generally any roof can be thatched but ideally, the pitch of the roof should be no less than 45 degrees so the roof can shed water faster. A roof with a lower pitch will not shed water as fast so will not have the same lifespan.