In traditional overlay multicast network, all peers are treated as equal regardless of their importance and contribution to the network. In this paper, we consider that each user may have different cost function depending on his privilege, delay to source, available bandwidth, etc. We propose a fully distributed and scalable protocol to construct an overlay tree to minimize the overall cost of the users. It uses aggregation to account for the total cost of one's descendants, and reduces tree cost by a continuous improvement process. Through simulation, we show that our protocol converges reasonably fast. By comparing with other schemes, our resultant overlay tree offers differentiated services to users by appropriately taking into account individual user cost functions.