Uncertainties are systematically considered and dealt with by applying probabilistic calculation methods, such as Monte Carlo simulations. When selecting appropriate distribution functions for input parameters, users are constantly faced with the issue of having to choose the "right" distribution function for the relevant parameter. Quantities of individual works play a crucial role for costing and pricing, but also for construction process and logistics planning purposes. Quantities stated by the client in its structural specifications are fraught with uncertainties owing to, for instance, incomplete plans at the time of specification, inaccurate calculations, or mere estimates. This is why actual quantities can either be greater or smaller than the specified quantities. This paper demonstrates how distribution functions can be derived from expert surveys delivering responses from actual construction practice. Specific reference is made to reinforcement works whilst distinguishing between public and private clients. The outcomes of the survey presented and discussed in this paper include descriptive data analyses as well as violin plots and fitted distribution functions.