You can get foam about 12 inches thick and frame it with plywood on top and 2x12 around the outside areas. Do a 4' by 8' piece for each section , then run 2x6 or 2x4 runners to hook them together. It helps to drive pipe to the lake bed to keep them from roaming after that. Each piece will hold two 200# men. Very cheap dock. Mine runs about 32 feet out in to the tank. Make sure the posts that hold it horizontally are not held tight so that the dock can not ride up and down as water levels vary.