We present some results of an ongoing research project where university engineering students were asked to construct videogames involving the use of physical systems models. The objective is to help them identify and understand the elements and concepts involved in the modelling process. That is, we use game design as a constructionist approach for promoting a modelling activity and the learning of the elements involved. In this paper, we focus on the case studies of two students, in their last year of studies, who built a videogame where they had to model liquid water behaviour while working within the restrictions of the game engine. By analysing students' written work and group discussions, we observed that students, through this videogame-building task, were able to deepen and refine how they conceive the process of mathematical modelling, in a fun and engaging way in which they were receptive and open to experimentation, and learned from other students, as well as from making mistakes.