The paper deals with the flat roof of low-energy buildings. The building sector is currently focusing on the maximum energy efficiency of buildings and related energy savings. At present, the building sector holds more than 40% of energy consumption and 36% production of greenhouse gas emissions. The whole sector of buildings uses more than 50% of the Earth's raw materials and produces approximately 50% of world waste. Roofs occupy about 20 25% of urban surfaces. The green construction practice expands and complements the classical building design concerns of economy, utility, durability, and comfort. According to the principles of sustainable development, future construction should be more focused on the reduction of pollution of the environment and the effective using of material resources. The aim of the contribution is multi-criteria assessment of the sustainability of the flat roofs. The purpose of this paper is to discuss the sustainability of six types of flat roofing systems in terms of environmental and thermal - technical parameters, financial and time requirements. The result of the contribution is the recommendation of the most suitable option for implementation.