The need for a better productivity of system engineering teams, as well as a better quality of products motivates the development of solutions to adapt methods to the project situation at hand. This is known as situational method engineering. In this paper we propose a generic process model to support the construction of a new method by assembling method chunks generated from different methods that are stored in a method base. The emphasis is on the guidance provided by the process model, as well as on the means underlying guidelines such as similarity measures and assembly operators. The process model is exemplified with a case study.