AreaBuilder

From fmepedia

AreaBuilder is a Workbench Transformer. The AreaBuilder transformer takes a set of topologically connected linework and creates polygon features where the linework forms closed shapes.

Polygons are output from the area port, and lines that are not part of a closed shape are output from an 'unused lines' port.

This transformer is capable of creating polygons, and also creating donuts (holes/islands) where warranted; in effect it is a combination of the PolygonBuilder and DonutBuilder transformers all in one.