|In construction projects supplements by modified or additional construction works are not uncommon. The client has to meet especially in the early phases of the project decision that may substantially affect the project progresses. These decisions are often taken under conditions of uncertainty and time pressure, or even not taken only. This lack of decision situation often results in a change in the decisions as the project continues. This leads to changed or additional services. Supplements, construction delays and construction cost increases then are no longer avoidable.The paper shows the importance of decision-making processes of a client. Therefore the importance of early development phases is set out, which include most of the major decisions of a construction project. Here, a study is presented that shows that the initial costs exceed the follow-up costs and not, as is often pointed out, vice versa. Furthermore, the difficulties of decisions that have to be taken in the context of a construction project are explained.