A window and door head flashing assembly is fabricated at a construction site to fit specific door or window widths. A center section which may be extruded with a sloped base, a rear flange, and a front lip. End caps may be provided to snap or glue on the center section. The end caps have a perpendicular fin which serves as an end dam to block the lateral movement of water. The assembly may be inverted for use as a sill pan. The center section may be cut to a desired length and installed over arched windows or doors by bending to shape as it is installed. For arched applications, a combination of rigid and flexible PVC may be coextruded to provide a desired cross sectional profile that is flexible enough to be bent around the arch, but stiff enough to retain its cross section for drainage.