Under aggressive miniaturization, unconventional digital switches rapidly come to light, which introduce new sources of variation in design parameters, and hence challenge the manufacturing process further. As a result, performance and power of manufactured hardware becomes greatly unpredictable. Characterizing variation-incurred unpredictability at early stages of the design necessitates dependable architecture-level models of variation, which distill device- and circuit-level details to accurately evaluate system-level implications. In this paper, we introduce a modular architecture-level model of parametric variation to address this challenge. As a case study, we refine our discussion to a representative class of emerging thin-channel switches, FinFETs.