I've been doing my own take on a waterfall braid recently.
I begin with a french braid near my right temple and slowly let it drape down to a braid on my left.
I only add hair from the top and let the hair around the nape of my neck fall loosely. So instead of adding hair with each plate like you would with a standard french braid I only add hair every other plate. So easy, it takes literally five minutes.