Abstract: A watertight and fire proof system for covering a roof is provided which comprises a plurality of tile elements which interlock in a horizontal direction relative the roof. The individual tiles can be interlocked and oriented relative each other to enable the selectable displacement of adjacent tile elements along a sloping direction of the roof which is perpendicular to the horizontal direction. An upper edge of a first one of the adjacent tile elements can be positioned at a different slope level of the roof relative an upper edge of a second one of the adjacent tile elements. Orientation of a first tile element relative a second tile element in the sloping direction is limited by contact between a lower flange of the first tile element and the abutting edge of the second tile element.