A roofer specializes in roof construction, concentrating on the application of materials that water proof an / or weather proof buildings, homes (residential construction), wineries, planter boxes, etc. Usually ply wood or solid boards are installed over the structure. Depending on the structure, it may be required to use other materials--such as steel panels, lightweight concrete, or specially designed material--as a substrate for the roofing materials to be installed on. The rafters, beams, and trusses are the frame or skeleton for the roof to be built upon. Naturally, a roofer must not be scared of heights and have good balance as well as carpentry skills. In Australia this type of carpenter is called a roof carpenter and in that country a roofer is someone who puts on the roof cladding (tiles, tin, etc.). In the USA a well trained roofer is called a journeyman. In California, if a journeyman wishes and has three consecutive years working in the field, he is eligible to pass a state test for a contractors license- state license.