Abstract: A roofing system for a sloped roof having a base with a generally horizontal top surface and a generally vertical edge has an internal gutter in its lower margin. The system includes a first flashing, that is attached to the base, having a lip which projects from the top surface of the base. The base is covered with sheets of flexible, thermally weldable roofing material with the top margin of each sheet being attached to the base and the bottom margin overlapping and welded to the adjoining sheet. The lower margin of the lowest sheet overlies the lip of the first flashing to form the gutter. A second flashing, which conformingly overlies the first flashing, is attached to the base over the sheet to clamp the margin of the sheet against the edge of the base. The margin of the lowermost sheet is pulled progressively tauter over the lip of the first flashing at the sides of the roof than at the downspout to make the gutter slope downwardly towards the downspout.