Project developers often have to choose between various alternatives when planning a new building. The expected cost, involved in design and construction, but also in later use, is a major criterion in decision making in the early stage of the project development. The result of a comparison of costs depends on the type of structure, its location and the national economical situation, including the cost of labor and material, but as well the readiness to accept hindrance and restrictions related to construction. The cost of realizing a structure is important, but cost evaluation should not be limited to the price of the structure as delivered to the client. A very important aspect as well is the cost in the period of use, to be paid for maintenance and energy. Furthermore, looking to the future, the structures would be more valuable if they would be adaptable to the changing wishes and ideas of the users. Moreover a new upcoming set of criteria arises from sustainability considerations, like the energy involved in production, the carbon footprint and the responsibility for saving resources. To further increase the complexity of defining the cost involved in a building, all those criteria are subject of change in time. That implies that “economy” as a criterion for decision making should not be limited to the narrowest sense of construction costs. It is more appropriate to focus on the “total cost of ownership”.