Floating Bottle island by Richie Sowa

In 1998, Richie Sowa build an island from over a quarter-million plastic bottles. A two-story house, solar oven, self-composting toilet and multiple beaches. It was destroyed but he is working on a new one.

Man (Re)Builds Mexican Island Paradise on 250,000 Recycled Floating Bottles | Ecoble

There is nothing new about this idea, besides from being really cool they do not last as long as your conventional slap of mud and rocks. You take old fishing nets and fill them with any stuff that floats then cover them with a thick layer of mud. You don't need a wooden frame. Sand doesn't seem to be very practical. The more mud you add the lower it gets so be careful with that :)