Roofing System for Buildings

A roofing system for buildings comprising a plurality of rafters to extend between two supporting locations and spaced apart across an area to be roofed, each rafter having an upper surface adapted with keying formations and two longitudinal sides from the bottom of each of which a lateral ledge extends, a plurality of infil units to be positioned, one unit between each two adjacent rafters, each unit being formed from an insulated panel of similar depth to the depth of a rafter and a support layer secured together, the support layer extending between and seating across adjacent ledges, and a tile to overlie each unit and to lap partially over each of the two adjacent rafters, and keying elements engaging and securing the tile to keying formation on the corresponding rafter, the keying formations on the upper surface of each rafter being formed of three grooves parallel to the longitudinal sides.