This paper describes a novel approach to constructing phonotactic models. The underlying theoretical approach to phonological description is the multisyllable approach in which multiple syllable classes are defined that reflect phonotactically idiosyncratic syllable subcategories. A new finite-state formalism, OFS Modelling, is used as a tool for encoding, automatically constructing and generalising phonotactic descriptions. Language-independent prototype models are constructed which are instantiated on the basis of data sets of phonological strings, and generalised with a clustering algorithm. The resulting approach enables the automatic construction of phonotactic models that encode arbitrarily close approximations of a language's set of attested phonological forms. The approach is applied to the construction of multi-syllable word-level phonotactic models for German, English and Dutch.