One argument in the discussion about the adoption of UML in industry is the supposedly large effort it takes to do modeling. Our study explores how the creation of UML models can be understood to consist of different cognitive activities: (i) designing: thinking about the design (ideation, key-design decision making), (ii) notation expression: expressing a design in a modeling notation and (iii) layouting: the spatial organization of model elements in a diagram. We explain that these different subactivities relate to different short-term and long-term benefits of modeling. In this study we present two controlled experiments with a total of 100 subjects creating models for a small system. In these experiments we focus on software models as represented through UML class diagram. Our results show that at least 56% of the effort spent on creating a class model is actually due to designing. Notation expression is around 41% of the model creation effort and layouting is in the order of 3%. This finding suggests that a significant part of creating models is devoted to design thinking about the problem.