When building a boat shed on a lake first draw the design of the shed then build a frame larger than the boat. Install some heavy duty corner brackets. Install a board every two feet across the length of the frame and attach brackets. Fix other boards across. Fix foam bullets on the underside of the frame in between the space then create a surface you can walk on. Build a second dock then fix three posts in the water on each side of the floating docks. Place the frame on the posts. Ensure the space between the docks is enough for the boat to fit then install the rafters and the roof.