Situational Method Engineering focuses on configuration of system development methods (SDMs) tuned to the situation of a project at hand. Situational methods are assembled from parts of existing SDMs, so-called method fragments, that are selected to match the project situation. The complex task of selecting appropriate method fragments and assembling them into a method requires effective automated support. This paper describes the architecture of a tool prototype offering such support. We present the structure of its central repository, a Method Base containing method fragments. The functions to store, select and assemble these method fragments are offered by a stratified Method Base Management System tool component, which is described as well.