Ancient civilizations had agriculture production in their metropolis but modern urban planning separated agriculture from cities, such as Chandigarh by Le Corbusier. At present, FAO estimates that urban agriculture produces food for a quarter of world’s population, reducing food transport, package and waste impact among others and improving food safety. Meanwhile, city governments and citizens are reinventing their roofs usage in order to take more advantage of them. Rooftop Greenhouses (RTGs) are an interesting option because they increase the scarce green area of the cities, create new agricultural spaces and promote food self-sufficiency in urban areas among other growing interests. RTGs are greenhouses located on the roof of the buildings that usually produce food using soil-less culture systems. These structures as well as the green façades called Vertical Farming (VF) are part of the “building-based Urban Agriculture (UA)”. In this sense, this article presents the first results of the research project Fertilecity, which aims to analyze, from a technological and sustainability approach, a new agricultural production system for Mediterranean urban areas through the integration of greenhouses on the roof of buildings. This innovative system is an integrated RTG (i-RTG) that includes energy, water and CO2 flows in the metabolism of the building. Multidisciplinary experts participate in this Fertilecity Project funded by the Spanish government. The first results of this research are: a review of the main experiences in UA; an environmental and economic life cycle analysis of implementing Rooftop Greenhouses (RTGs) in the Barcelona area; and the construction of the ICTA Rooftop Greenhouse Lab, which is an i-RTG located near Barcelona. This article will explain the objectives of this research project, which aims to demonstrate the potential of i-RTGs and quantify their environmental, economic and social benefits, as well as study how they can change the image of our cities.