cap 24 of channel section is applied over the exposed end edges of the panels 2 and the connector channel 6 the panels 2 with the integral upstanding lips 4 may be produced in a number of standard widths which are cut to required length for use although it is desirable to design the structure so that each section of the structure can accommodate a complete panel of standard width in some situations an end section of the structure may be of a width less than a standard width in that case the glazing panel for use in that section can be cut to the required width leaving a small excess portion which can be manually bent upwardly to form a projecting lip by partially cutting through the thickness of the panel to facilitate bending that lip can then be secured to the extension 14 of the end most bar 10 in the structure using the connector channel as previously described as mention previously although the preferred embodiment is particularly suitable for use with existing danpalon panels which are polycarbonate panels and connector channels the embodiment is not confined specifically to use with those panels and the associated connector channels other glazing panels formed from polycarbonate sheeting or other suitable plastic sheeting and having upstanding lips along their longitudinal edges may alternatively be used likewise other forms of connector which fit over the lips to secure the lips to the bar to provide a watertight seal can be used it will be understood that the system in accordance with the invention in addition to permitting increased roof spans without the need for.