Which of the following is NOT a common metal used for roof flashing?

Plastic is the option that is not a common metal used for roof flashing. Roof flashing typically requires materials that can withstand the elements and provide a durable barrier against water infiltration. Metals like galvanized steel, lead, and stainless steel are commonly used for flashing due to their strength, resistance to corrosion, and longevity. They can be molded and shaped effectively to create watertight seals around joints, penetrations, and edges of roofing structures.

Plastic, while it might be used in some specific applications for roofing or plumbing, does not possess the same durability and robustness as metal options. It may not maintain its integrity under extreme temperature fluctuations or during exposure to ultraviolet light over time, making it less suitable as a flashing material. This is why plastic is not considered a conventional choice for roof flashing compared to the reliable properties of various metals.