Abstract: A metal building panel, such as a roof panel, has its longitudinal edges roll-formed to define integral male and female edge formations. Each edge formation includes an upstanding flange, a return flange angularly disposed with respect to the upstanding flange such that the distal portion of the return flange is spaced from the upstanding flange a distance greater than the distances other portions of the return flange are spaced from the upstanding flange. Each of the return flanges joins with a reentrant rib. The reentrant rib of the female edge formation joins with a return lip. Adjoining male and female edge formations of a pair of such panels may be readily inter-engaged to form a snap-lock connection. If desired, a further mechanically seamed lock may be obtained by the application of squeezing forces to the inter-engaged male and female edge formations of a pair of such panels.