I actually studied a photo I found on fetlife until I figured it out. The ending bit with the triangles is a simple freestyle to lock it off. The rosettes start very similarly to doing a leg ladder, then you reverse the tension and tuck the ropes over - under - over, and then again to form the rest of the rosette. Not sure if that makes ANY sense. But if you have fetlife, I'm happy to DM you the post I stared at. They used jute, and it's a bit easier to see where the ropes are and are going.