Semi-Weathering Gray-Green Roofing Slate is a popular Vermont roofing material. This roofing slate can “weather”, meaning it will take on brownish tones over time. Because of its excellent properties and performance, warm coloration after weathering and economical price, this natural Vermont slate is frequently used for residential and institutional projects. Semi-Weathering Gray-Green Roofing Slate is available in many sizes and thicknesses.