Flat stones are laid so they shed water outwards. Stone shelters on the French Causses have been roofed like this for thousands of years. The roof is watertight and lasts for hundreds of years. I have seen a similar method used in West Wales on megalithic cliff shelters.
About this Blog
My travels through contemporary France in search of Richard the Lionheart and relics of his 12th century kingdom.
Paris, Rouen then the Duchy of Aquitaine, seeking useful detail and atmosphere for the second novel in the Lionheart Chronicles.