Authentic Slate is very beautiful, strong, and long lasting. It is also expensive and there are not too many light weight options. When there is a need to consider budget and weight, there are some alternatives to achieving the look of Slate.
DaVinci Roofscapes offers Synthetic Slate Options that are Lightweight and Class A Fire Rated. There are also more budget friendly options such as Boral Concrete Saxony 900. For structures that require a lightweight concrete tile, Saxony 600 will work and at 570 lb per 100 sq ft you will not need to have the structure assessed by an engineer prior to installation. (Any product over 600 lb per 100 sq ft being considered on a reroof will likely need to be assessed by an engineer.) There are also asphalt shingles that are designed to look like slate so you can have all of the benefits of an asphalt shingle and still get a high end slate look.