If you open the Ruby Console before running the plugin (Window >> Ruby Console), it will display some useful information along with any errors that might occur. Depending on the shapefile dataset, the range of co-ordinate information may need to be scaled substantially. SketchUp cannot create an edge that is smaller than 0.001" in length. The workaround for this is to scale the geometry up before using it and then scale it back down when done. The plugin makes no assumptions about units and uses the data as raw units created as inches. The second issue is that large datasets may have so many polygons made up of so many edges that your computer may not be able to realistically handle it (mileage varies widely). This is the purpose of providing a limit on the number of polygons as well as providing a limit on the constraining bounding box. This is the purpose of creating the grid file to help determine the bounding box limit for any given run. If you run the plugin for the LARIAC buildings and use the following values, you should get a successful result:
xmin = 6483101 ymin = 1839530 xmax = 6487005 ymax = 1843435 scale = 1
For other shapefiles, like those available from GEOFABRIK, I ran a sample input with the original bounding box for the first 10,000-odd polygons using a scale factor of 100,000. This gave me a decent idea of where in the x/y space the data lies. Measuring from the origin with the tape measure gave me the xmin/ymin-xmax/ymax values I needed to restrict the data. Let me know how it works out for you … this is still a work in progress.