The diagrid structural system has been widely used for recent tall buildings due to the structural efficiency and aesthetic potential provided by the unique geometric configuration of the system. This project presents a stiffness-based design methodology for determining preliminary member sizes of R.C.C. diagrid structures for a G+14 story building using ETABS 2015. The methodology is applied to the diagrid to determine the optimal grid configuration of the diagrid structure and further its comparison with conventional R.C.C structure. Analysis of G+14 story building with perimeter diagrid of 630,660,690 is carried out by Equivalent Static Method. The comparison of analysis of results in terms of top story displacement, story drift, story stiffness, story overturning moment are presented.