Process flexibility has evolved into a desired corporate capability as it promises to cope with demand uncertainty and variety. Particularly service processes have a high intrinsic need for flexibility. Many approaches have been proposed to determine the business value and an appropriate level of flexibility for service processes. Most of these approaches focus on a distinct flexibility type and on single projects for implementing flexible service processes. The question how to reasonably combine flexibility projects has not been addressed yet. Moreover, most approaches do not conduct a full-fledged economic analysis of process flexibility. We therefore propose a decision model that helps determine an optimal flexibility roadmap, i.e., a scheduled portfolio of flexibility projects with different effects on service processes. The decision model accounts for different request types (i.e., runners, repeaters, and strangers), different capacity types (i.e., internal, external, dedicated, and flexible), different flexibility types (i.e., volume and functional), and related project archetypes. The decision model was evaluated using feature comparison, prototype construction, and a demonstration example including an extensive scenario analysis