19 PORTABLE BUILDINGS; CANOPIES AND STRUCTURES; GUTTERS AND CEILINGS, ALL MADE WHOLLY OR PRINCIPALLY OF NON-METALLIC MATERIALS; AND PARTS AND FITTINGS FOR ALL THE AFORESAID GOODS; AND NON-METALLIC BUILDING MATERIALS-NAMELY, DOORS, DOORFRAMES, WINDOWS, WINDOW FRAMES, ROOF-SUPPORTS, BLINDS, SHUTTERS, GUTTERS, DRAIN GUTTERS, JOISTS, BEAMS, WINDOW AND DOOR LINTELS, VENTILATORS, ROOF WINDOWS AND ROOF LADDERS