The offset tool is a tool in Google Sketchup that allows users to select a surface, and drag the edges of a new face around it with the same shape. The clearence between the old and new edges is everywhere the same, which makes it effective to produce rooflines. If you drag the new edges to far away, the new face will get distorted by intersecting edges. If the original surface has a lot of short edges, this is more likely to happen.
In the following example, an extraordinary surface with both inward as outward corners was created. The user creates a new face around it with an offset of 0,278 meters. In the third image measurements are shown, explaining that the clearence between the original face and the new edges, is 0,278m everywhere.