Cities of the global North are increasingly trying to green their spaces, notably by encouraging urban agriculture (UA) development in vacant spaces such as rooftops. Different strategies can be used by cities to achieve this goal. We studied Paris's international call for projects (CFP), "Les Parisculteurs", which aims to provide public and private rooftops to urban farmers. This study seeks to examine the relevance of urban rooftop farming (URF) in the city of Paris in view of its specificities and to understand the management of the CFP which is currently an innovative way to develop urban rooftop farming. We will show how this CFP tends to respond to the city of Paris's challenges regarding UA. The comprehensive analysis of this CFP is based on the results of an 11-month participatory research work: we participated in the study and the setting up of the CFP by being part of the "Assistant to the Contracting Authority" (ACA), commissioned by the City of Paris. It appears, inter alia, that this CFP lifted several barriers blocking projects installations, is a way to green the city quickly and in a cost-effective way, promotes the diversity of the projects of UA and allows the City of Paris to test technical and regulatory limits of UA on existing buildings. It was also pointed out that developing UA by providing lands on rooftops without financing the winning projects had strongly encouraged the professionalization of urban agriculture in Paris. To conclude, CFP can be a relevant way for a collectivity to encourage urban farming but it cannot be a systematic solution as it is adapted to a specific context and it carries the risk to develop projects which are disconnected from their local environment.