In the present study flyash is used as a raw material to replace clay for making flyash brick tiles to be used in roof terracing works in buildings. The aim of present investigation is to find out a combination of materials with flyash as main constituent and coarse sand, fine sand, stone dust and lime as secondary constituents to give minimum permeability and maximum compressive strength. The percentage of cement was kept constant ie 10% throughout the experiment for economic considerations. The work has been carried out in two stages. In the first stage efforts have been made to find out various combinations based on pure flyash mixed with fine and coarse sand, flyash mixed with lime ie treated flyash with fine and coarse sand and treated flyash mixed with stone dust and fine sand to give minimum permeability. In the second stage three types of flyash brick tiles were made with the combinations giving least permeability and tested for compressive strength. The strength achieved was less than the clay brick tiles but sufficient enough to be used in roof terracing works. As flyash is available free of cost at the thermal power houses dump yards, the tiles manufactured by using flyash are cost effective compare to the clay tiles more over there is a saving of irrigable top soil.