This paper discusses some tools that may assist designers to determine the building system which is “best”. The choice of building structural system may be treated as a constrained optimization problem considering uncertainty. Real life constraints affecting the design include owner requirements (e.g. functionality, aesthetics), political and safety considerations (such as height limits, performance, waste disposal criteria), cultural/logistic considerations (e.g. skill sets for construction, material availability), as well as cost. These decisions may be made in a number of ways. Decision support tools using both probabilistic methods (for buildings in seismic and non-seismic design zones), as well as using subjective quantitative analysis, are described. Examples of both are provided for the selection of different building systems. It is shown that both probabilistic design tools and subjective quantitative analysis tools have strengths and weaknesses and often they are used together. Since both methods are based on many assumptions, interpretation of the outputs from such tools should acknowledge such assumptions.