* Make sure the the measures in the [http://img360.imageshack.us/img360/5919/guidesv6.jpg lower right box] are in meters, if not go to [http://img360.imageshack.us/img360/116/preferencesmv1.jpg preferences] and set it to metric meters 3D in template tab.
* Now select make a square of 4x4 meters. Just start drawing a square and type 4,4 then hit enter.
* Copy the squares to make a grid
* Download the needed models from Wurm on the Sketchup Warehouse.