Want the look of slate without the cost or weight? The people who make Authentic Roo f take 100% recycled and re-engineered polymers and rubber materials, mix them together, then injection-mold them into dark gray, 12x18-inch pieces patterned after 100-year-old slates. The rubber makes the slates flexible, while the plastic adds strength. Authentic Roof slates weigh about the same as equally-sized asphalt shingles, cut easily with a utility knife, and are fastened to a standard plywood roof deck with 11/2-inch galvanized roofing nails. (No batten strips are needed.) The slates can be installed with up to a 7-inch exposure, and the tabs at each end maintain a 1/4-inch spacing between slates. The cost is approximately $250 per square and $2.50