In a multiagent system, coalition formation is a coordination method for agents aiming to form groups of interest. In this paper, we focus on the particular context where agents are self-interested and plan their activities. We develop a new coalition formation model that uses the plans of the agents to guide the search for the coalitions and analyzes the coalition proposals already suggested by other agents in order to derive their preferences. This eases the negotiation for the coalitions. We analyse and develop the constraints that should be enforced on self-interested agents in order to form suitable coalitions which guarantee significant solution concepts. In addition, we detail in this paper our coalition formation mechanism, we experiment and evaluate it.