Abstract: A plastic covered building structure comprised of a metal frame supporting superimposed layers of plastic sheets having an inflated area between the sheets providing insulation to the interior of the structure. The superimposed plastic sheets are secured to the frame by means of longitudinally extending rails having longitudinally extending upwardly concave portions and complementary clamping rods adapted to secure the edges of the superimposed plastic sheets between the rods and the upwardly concave portions of the rail. The rails are adapted to receive clamping members at any point along the length of the rails to clamp the rods into the upwardly concave portions.