A sheet of light transmitting polycarbonate is vacuum-formed to produce a lower skylight glazing or pane, a surrounding curb portion and a surrounding flange or flashing portion projecting outwardly from the curb portion. The curb portion has a peripheral rim surface and a lower step surface, and an upper pane of glass or plastic has a peripheral portion sealed to the rim surface. Additional panes of plastic sheets may be sealed to the peripheral portion of the upper pane and to the step surface to provide increased thermal insulation. Parallel ribs are formed in the flashing portion, and strips of rigid plastic insulation foam and wood trim are bonded by adhesive to each other and to the inner surfaces of the curb portion.