Modelling and designing business processes has become a crucial activity for companies in the last 20 years. As a consequence, multiple workflow modelling notations were proposed. Business Process Modelling Notation (BPMN) is one of them and is now considered as the de facto standard for process modelling. The BPMN notation offers a rich syntax that requires a certain level of expertise before being able to write correct and well-structured processes corresponding to some expected requirements. The BPMN modelling phase can thus be tedious and error-prone if carried out by non-experts. The main goal of the approach presented in this paper is to help users modelling BPMN processes. To do so, the approach takes as input the requirements of the user in a textual format informally describing the tasks and their ordering constraints, and generates as output a BPMN process satisfying them. The solution has been implemented as a tool that was applied on a large number of examples for evaluation purposes.