Recent years have witnessed the growing usage of cloud computing services in different aspects as it promises a wide change in how information is stored and used to run applications. This emerging trend has rapidly become a new computing paradigm of great interest for the software practitioner community. All cloud based applications needs to be delivered in higher level of quality than conventional applications due to the wide risk it faces. As cloud based applications are highly dynamic and versatile, therefore conditions can alter very quickly based on changes in user requirements. However, while searching for a standardized quality metric for cloud based applications, it has become evident that there is a dire need of a unified approach in this regard. From software quality perspective, the final quality of the cloud services is directly influenced by the quality of each service. Therefore, there is a high demand for devising a quality model for cloud application developers to measure and evaluate these services. This research critically evaluates the current quality models for cloud based applications and how these are implemented, deployed and integrated within various cloud services. Finally, by identifying gaps and current requirements, authors propose a refined quality of service engineering model for the cloud computing applications based on the existing cloud platforms.