We consider the problem of multirate network design with point-to-multipoint communications. We give a mathematical formulation for this problem. Using approximations, we show that traffic concentration on a small number of links significantly reduces the cost of the network. We then propose a heuristic based on the traffic concentration principle to solve the network design problem approximately. Because this heuristic no longer requires advanced knowledge of demand matrices, we explain how it can be used as the basis for real-time design procedures. By means of numerical results, we show that this heuristic yields nearly optimal solutions.