Differential equations (DEs) are a powerful tool for modeling real-world contexts. Most research in this area has examined students' understanding and reasoning with pre-packaged DEs, with little attention being given to setting up sophisticated DEs to model complicated real-world situations. This study contributes through a collective case study on how individual students constructed DEs for various real-world systems, including a mechanical, a hydraulic, and an electrical system. We examined the students' readouts (how they "read" a context), their inferential nets (inferences across knowledge resources), and their strategies (what guided their work), according to coordination class theory. Our study contributes the foundation of a knowledge base in students' DE modeling that further research and teaching work can build on.