I analyzed all the Free to play model of Dragon City, a mobile and facebook game developed by Social Point. The purpose of the analysis is to understand how a free to play model works. For this, I watched the gameplay of the game, the 3C, the core loop, how the player progresses, the special features and the economic system. Then the most important was to understand the acquisition, retention and monetization in the game, which defines the genre Free to Play. This exercise allowed me to know how I could think the gameplay of my Builder: Blooming sky. I had to work on the balancing and using the ARM model, I had an idea of how to proceed. The document is in French but I can explain it in English for more information!