When selecting a site, consider the available materials. You may be able to use trees if they are in the right position for building this structure.
Look for four trees positioned in a rectangle. If you cannot find the right layout of trees, cut four poles and drive them firmly into the ground to form your rectangle. They should be far enough apart and strong enough to support your height and weight, to include equipment.
Cut additional poles that span the width of the rectangle. They must also be strong enough to support your weight. Lay them across the two side poles and secure them with any lashings available. Be sure everything is high enough above the ground or water to allow for tides and high water.
Cover the sticks on the top of the bed frame with a coat, sleeping bag, or broad leaves and/or grass. Whatever softer, dry materials are available to make your sleeping surface.