A metal roof is a roofing system featuring metal pieces or tiles exhibiting corrosion resistance, impermeability to water, and long life. It is a component of the building envelope. The metal pieces may be a covering on a structural, non-waterproof roof, or they could be self-supporting sheets. History Lead and Copper have played a significant role in architecture for thousands of years (see: copper in architecture). Lead was one of the first and easiest metals to smelt and with a low melting point, could be easily formed watertight. As a by-product of silver smelting, in Roman times it was readily available and relatively cheap. After the 2019 fire melted the lead roof of Notre-Dame de Paris, it was decided to restore the lead as it had been. In the 3rd century B.C., copper roof shingles were installed atop the Lovamahapaya Temple in Sri Lanka. The Romans used copper as roof covering for the Pantheon in 27 B.C. Centuries later, copper and its alloys were integral in European medieval architecture. The copper roof of St. Mary's Cathedral, Hildesheim, installed in 1280 A.D., survived until its destruction during bombings in World War II. The roof at Kronborg, one of Northern Europe's most important Renaissance castles (immortalized as Elsinore Castle in Shakespeare’s Hamlet) was installed in 1585 A.D. The copper on the tower was renovated in 2009. When iron smelting became widespread in the early 19th century, although the smelting process was complicated, ore was so plentiful that iron became cheaper than lead, and much much cheaper than copper. It was soon learned that the corrosion that usually destroyed iron could be stopped or at least slowed by dipping the hot iron sheets into molten tin or zinc, forming a metallurgically-bonded coating which protected it. Terne, an iron plate dipped into a solder of 80-90% lead with only the remainder tin, was cheaper than tinplate made in the same way, and the lead was more resistant in long-term outside use than tin or zinc alone. Terne became popular for roofs and weather-resistant farm items. In 1829, Henry Palmer, engineer of the London Dock Company, patented "indented or corrugated metallic sheets" which added additional stiffness to bending in one direction in the manner of a beam. This allowed the sheet iron to be self-supporting when used as a roof; a contemporary account praised the material as "the lightest and strongest roof (for its weight)