Abstract: A roof covering installation includes a pair of side panels having a shape conforming with the sail panels of the vehicle body and a center panel preformed to the contour of the roof panel and adapted to fill the space between the side panels. The side panels and center panel have edge portions which are adapted for mating overlap and are joined together to provide a substrate assembly having a width gauged to the lateral spacing of the sail panels to precisely overlie the roof and sail panels irrespective of dimensional variation in the width of the vehicle body. The roof covering is adhesively secured to the substrate assembly in an off-line assembly, after which the substrate assembly is mounted and secured on the vehicle.