second mating means part 22 on panel 10 b fits into the first mating means part 18 of panel 10 a forming the vertical standing seam a longitudinal strip or band 24 of a resilient sealent of gasket can be applied to one of the mating faces of the first or the second mating means parts 18 22 to render the seam water tight if this strip or band 24 is adhered to one of the mating means parts 18 22 it should not be adhered to the other as adhesion to both the first and second mating means parts 18 22 could result in restraining the panels from expansion in the longitudinal direction causing stresses in the panel however it is desirable that the strip or band 24 be maintained in compression by the mating of parts 18 22 fig1 and 2 also show another feature of the panel 10 each side edge is also provided with a groove or channel 26 intended to receive a tongue of a clip as described in more detailed below for structural integrity as well as for facilitating the guiding of the panels 10 into place each groove or channel 26 has a pair of built up gussets 28 30 one of the gussets above the channel and the other below the channel also notable in fig2 is the vertical channel 32 available for receiving an upstanding member of the clip used to secure the panel assembly to.