Abstract: A building panel which can be fabricated on site to any desired length, comprising a continuous strip having two mutually interlocking edge structures running the full length of the panel, one edge structure being adapted to be fastened to the underlying roof and including an outer flange with spaced slots through which a nail or screw can be used to fasten the panel, an upwardly projecting lengthwise first ridge with a rounded upper portion, an S-shaped recess spaced inwardly from the first ridge and running lengthwise of the panel, and the other edge structure including an outer flange adapted to be inserted into the S-shaped recess of the next adjacent panel, and an upwardly projecting lengthwise second ridge adapted to overlie the first ridge of the next adjacent panel.