Buildings of commercial and non commercial purpose consume large amount of electricity. Therefore to design a green or smart city the biggest challenge for a designer is to convert all buildings from energy consumer to energy producer. Recent study reveals that most of the designer prefer solar energy for smart city development because it can be housed in a limited space and is characterized as pollution free, environment friendly, sustainable as well as noise-free source of electricity. Among the photovoltaic technologies rooftop and building integrated photovoltaic (BIPV) technology are the commonly adopted technologies for green building. This paper presents a comparative study of cost-benefit analysis between roof top solar and BIPV technology for making a green campus of University of Engineering and Management, Kolkata, phase 1. The result of the study will help designer to select proper photovoltaic technology to develop a green city in more cost effective way.