Composite applications are developed by integrating independent web services and deployed in a dynamic cloud based environment. An ability to modify the composite applications in response to changing business needs significantly contributes to agility of enterprise information systems. Deployment and execution in the cloud based environment allows to requisition resources necessary for efficient execution of the composite applications. However, properties of the composite applications directly depend upon characteristics of external services used and environmental factors, which in the case of public networks, exhibit high degree of variability. In order to address this issue, the objective of this paper is to develop a simulation and business process modelling based platform for evaluation of composite applications to ensure that the applications developed deliver expected performance. The combined approach allows for comprehensive evaluation subject to stochastic and dynamic factors, and the platform integration reduces the modelling overhead. Application of the simulation platform is demonstrated using an example of designing a composite application for a taxi call center.