Ficus are easy to develop into root-over-rock designs as they have aggressive roots that tolerate gradual exposture to air and the roots really do well growing over rocks. The photo is of a Ficus burkei ‘puberula’ cutting that was placed on the rock, roots wraped to keep them tight on the rock and then planted deeply so the roots were not exposed to air. Gradually over some years the soil was removed from the rock and the roots exposed. Done repeatedly the rock was elevated and more of the roots showing. This picture is about 10 years or so after the procedure was started.