In this paper, Portland cement was used as cementitious material and expanded perlite was used as insulation material. Fatty acid salt water repellent was also added to make this new thermal insulation, waterproof and light weight roof building material. It can be cast onto flat roof during construction or made into tiles and laid onto sloping roofs. This new roof building material had short construction period and can be completed in a one-time process. It may replace conventional construction method of applying insulation and waterproof materials separately.