Nowadays, a lot is invested in planning the cost-effectiveness of building construction and its lifespan. First of all, with proper maintenance and smart forecasting of future construction costs, the investor can save large sums. In another words it should be respected that each building has its own service life. Therefore, in this thesis, using several methods of analysis (net present values, sensitivity analysis, factor methods) will show their significant impact on future costs. Indicative costs will be shown, such as: costs of use, legally prescribed periodic inspections, worn-out materials and elements, periodic repairs, etc. All the above costs can be expected by the investor, but with the help of the previously mentioned methods he could prepare his investment for construction part and its functioning after it was built. In addition to showing the discount rate that may vary, its role at the time the building is planned and at the time of its completion will be clarified. In other words, the value of our money is not the same in the present and the future. Also, with the help of tables, graphs and descriptions an attempt will be made to approach the problems, but also the solutions in the analysis of the projected service life. The results of the methods will be presented at different time intervals, which will show the differences between good and bad life planning, and indicate the improvements that can be applied in today's management of public buildings. In the preparation of this thesis, real data from the construction profession will be used in order to show as faithfully as possible the impact of methods and the importance of cost planning.