Green roof of a building is partially or completely enfolded with vegetation and its associated components. It promotes the sustainability and comfort of buildings. This study determines the most suitable growing substrate by investigating organic wastes of Sawdust, Wood bark, Bio char, Coir, Compost and Base medium (fertilizer + potting mix) through comparing density, moisture content, drought resistance, thermal resistance, vegetation growth, pH, electric conductivity (EC) and nutrients. Unlike previous studies on green roof substrates, we have investigated chemical parameters and showed its importance on substrate selection. Unique mathematical concepts were used to find thermal conductivity and EC of specimens in our research. Preliminary study results shows that the most substrate composition includes 60% selected substrate and 40% base medium. Base medium (90:10) has highest bearing capacity to withstand external loads including vegetation and other imposed loads. Sawdust (60:40) exhibited consisted the least saturated unit weight, dry unit weight and the highest moisture content. In terms of drought resistance and vegetation growth, Bio char (60:40) was exceptional. Wood bark (60:40) exhibited the most convincing thermal resistance. The best characteristics in terms of pH, EC and nutrient content were exhibited by Sawdust (60:40), Coir (60:40) and Compost (60:40) correspondingly. Based on final ratings by considering all the experimental results, Coir (60:40) have emerged as the optimum growing medium in terms of physical and chemical properties. This experimental study results would provide a strong framework for construction industries to enhance sustainable green roof constructions with best practice in substrate selection.