is cut away i e the rim ends at 32a and 32b as best seen in fig1 the end 24a of the bent back portion 24 lies against the inner surface of the left hand end of the lip 30 along its lower edge the panel 12 has a downwardly projectinglip 34 fig3 that is bent back on itself at 36 the flat portion 36 extending into an inwardly and downwardly curved portion 38 that defines a groove 40 while the lip 34 extends the full length of the panel 12 the portions 36 and 38 and hence the groove 40 terminate at 38a and 38b fig2 at the lower left hand corner of each shingle as seen in fig1 the end 24b of the portion 24 lies against the outer surface of the lip 34 the shape of the groove 40 is such see especially fig6 and 7 i e with a mouth 42 of restricted width d1 that the rim 32 of one shingle 10a width d2 slightly greater than d1 can be snapped resiliently into place and retained in the groove 40 of an adjacent shingle 10b as shown in fig7 in this manner the bottom edge of one shingle 10b can be firmly interlocked with the upper edge of an adjacent shingle 10a fig8 and 9 show the end to end interlocking of a pair of such shingles here designated 10c and 10d the lip 20 on the right hand end of the shingle 10c engaging in the space between the bent parts 18 and 24 of the shingle 10d while.