The study investigates the structural behavior of low cost roof system of steel frame and thermo-stone blocks. The sustainability engineering requirements were considered in terms of the efficiency of thermal insulation and reduce energy consumption and the use of environmentally friendly materials. The roof construction was tested by examining the horizontal and vertical modes of thermo-stone blocks after laboratory tests and calculation of stresses. The results showed that carrying the vertical loads in the horizontal position around (18.5) tonnes/m2, while in the vertical position approximately (185) tonnes/m2, or about ten times. Cracks or damages were not appearing in the vertical position of thermo-stone under loads while failure occurs in thermo-stone blocks in horizontal position.