An apparatus for assembling a plurality of sheet articles into a document includes a plurality of individual sheet input paths along which one or more sheet articles can be advanced, and a central accumulation area for accumulating the sheet articles. The central accumulation area includes a single-level accumulation surface for receiving one or more sheet articles advanced from each individual sheet input path and accumulating the sheet articles in a single stack. The central accumulation area can receive sheet articles from two or more different directions. The sheet articles can optionally be staged for accumulation into subsets prior to advancement to the central accumulation area. The central accumulation area advances the assembled document into an output path.