To ensure correctness and performance of real-time embedded systems, early evaluation of properties is needed. Based on design experience for real-time systems and using the concepts of the POOSL language, we introduce modelling patterns that allow easy composition of models for design space exploration. These patterns cover different types of real-time tasks, resources and mappings, and include also aspects that are usually ignored in classical analysis approaches, like task activation latency or execution context switches. The construction of system models can be done by integrating the necessary patterns, as illustrated in two case studies.