The successful energy design of buildings requires that special attention be paid to the conceptual stage. However, it is a difficult task to find the most promising design alternatives satisfying several conflicting criteria. This thesis presents a simple multi-criteria decisions analysis method that could assist designers in green building design. Variables in the model include those alternatives that are common options when a residential building is to be constructed. The individual components that are considered are the building envelope, heating, ventilation and air conditioning (HVAC) system, service water heating, power and lighting. The key actors, objectives and methodology of multi-criteria decisions analysis are presented and finally a case study for a residential building in Athens is performed. The criteria by which to evaluate each building component of the newly built construction were identified by the decision-makers. Subsequently, decision frameworks for the selection of roof, walls, windows, heating system, energy source for heating system, power source, lighting and service water heating system were built. The method is followed step-by-step to conclude on the optimal building components based on their score. Due to the equal scoring of the windows and an inapplicable combination of electric underfloor heating with air-to-water heat pump, the method is characterized by low accuracy. The fact that the building components have been treated individually sets the method as a basic one and indicates that a more complex one should be preferred when more trustworthy results are needed.