Non-metallic building materials, namely, roof tiles made of clay and fittings for roofing in the nature of slates, underlays, felts, asphalt, shingles, sealants, non-metallic gutters, ridge and hip caps, valley tubes, flashing, ventilation units, vent pipes, windows, skylights, insulation, abutments, eaves, snow guards, non-metallic roof outlets, and safety systems, namely, walkways and roof steps