One of the open research problems in the area of overlay networks is the creation of an adequate network topology and a proper network model. Current models mainly focus on traffic demands and loads between the nodes. However it is more challenging to find a model which supports scalability, adaptability and robustness in a heterogeneous environment. We introduce a new three-tier model based on regular-graph theory called STree and its two-stage joining mechanism. We compare STree with other models such as NICE, DTree and HMRB. Our results suggest that STree is a robust and scalable model for overlay networks in large, dynamic and heterogeneous environments.