The subject of the master's thesis is a conceptual architectural design for the Kovinar shopping centre in Ribnica. Based on the conceptual project we have received, we are trying to optimise the concept of the building envelope in terms of indoor illumination with daylight, and at the same time reduce the use of energy for heating and cooling purposes. At first we reviewed relevant professional literature containing studies dealing with architectural measures applied to building envelopes with the purpose of reducing energy use, and improving illumination of rooms with daylight, which was our purpose as well. In the practical part of the thesis we analysed illumination with daylight offered by the proposed conceptual design, using a computer 3D model, and designed an optimized model in terms of the amount and the layout of the glazing. We established that a combination of glazing on both the facade and the roof was optimal. We continued with simulations of energy use at the model with optimised glazing, and defined the adequate construction and physical properties of both transparent and non-transparent structures of building envelopes. The total glazing area of the optimised model was smaller by 33.10%, compared to the glazing area of the initial model, while the indoor surface with adequate daylight illumination increased by up to 36%, while the adequately illuminated surfaces diminished by 13% only in one case. The anticipated required cumulative energy of the building amounted to 495491 MJ (267,25 MJ/m2) for the initial model, while for the model with optimized glazing it amounted to 407511 MJ (257,67 MJ/m2), resulting in saving of 18% of the cumulative energy of the building. The total annually required energy for heating of the building for the initial model was 272684 MJ (172,15 MJ/m2), and 280760 MJ (177,25 MJ/m2) for the optimised model. The annually required energy for cooling purposes for the initial model amounted to 222807 MJ (140,66 MJ/m2), and to 126751 MJ (80,01 MJ/m2) for the optimised model. The model with optimised glazing was subjected to some other measures applied to the building envelope; thus compliance with all the requirements of the LEED certification system for illumination of buildings was achieved.