Since the use of metal roofing is growing, more and more builders and homeowners are faced with the choice between steel, aluminum, and copper. Still another choice exists: For those whose budget can stretch to about $7,000 a square, there’s always gold. “We’ve done a lot of roofs over the years — a lot of religious structures and a lot of government buildings,” says Michael Kramer, president and founder of The Gilders’ Studio in Olney, Md., one of the four or five companies in the United States that specializes in gilding roofs. “We’ve also done some very highend private residences.” An ounce of gold will cover about 100 square feet of roof. The standard size for a leaf