Nowadays, the cloud computing industry is enjoying an exponential growth, where several cloud service providers compete to be one of the market leaders. Usually, providers offering similar services use different non-functional attributes to describe them. Thus, given the heterogeneity and diversity of services descriptions, the selection process of the appropriate cloud service becomes challenging. Architects no longer know what criteria to use to make the suitable cloud services selection. In this paper, we highlight the challenge of identifying key elements of comparisons and their relationship for selecting cloud services. Further, we propose a methodology to solve this issue based on real data available from service providers and benchmark work. Our methodology is validated based on two case studies of cloud relational databases and cloud queuing services.