Depends on what you want from your lawn. A toposurface with grass material applied seems a good option.
Toposurfaces can be found under "Massing & Site"
Louis
Please mention Revit version, especially when uploading Revit files.
Well, Revit does not have a "Lawn" tool.
You could turn your topo surface green.
You could model-in-place something, and turn it green.
You could import an image of a lawn.