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MOST COMMERCIAL BUILDINGS IN USA HAVE ROOFS (FLAT) WITH LAYERS OF ROOFING COVERED WITH HOT TAR AND SMALL STONE..SO OF COURSE THE SUPPORTS MUST BE STEEL COLUMNS AND TRUSS
WE LIVE IN A COUNTRY THAT CAN NOT MANAGE EVEN WASTE.EVERY PIECE OF LAND COVERED WITH LITTLE BUSH IS SEEN AS PLACE OF CONVINIENCE.AND UR TALKING ABOUT STEEL COLUMNS AND TRUSS.GIVE US A BREAK