Abstract: A roof valley structure including a unitary panel of durable polypropylene-rubber material having a longitudinal flexure section including a large fold through its center, interlocking ridges spared on each side of the flexure section, and a plurality of spaced parallel longitudinal ribs on the outside of each interlocking ridge. The ribs, folds and ridges are reduced in size slightly at one end of each panel to permit one panel to overlie and interlock with a panel lower on the roof valley. Another embodiment connects two or more such panels together by means of a horizontal fold thereby making it possible to fold the panels together for packing and shipping. The folds in the flexure sections of adjacent panels are designed to nest together when the two panels are folded. Special nailing sections are shown which compensate for thermal expansion and contraction.