I can get a 10’ by 10’ tarp with tie-downs down the middle and rings in the middle of each side and at the corners. So I could make a shelf with a back wall about three feet off the ground, tied off at six points and with three more lines holding the back wall up or folded forward at some angle. Another way is to make a diagonal and use one corner as the shelf, then a quad-shaped back wall and a whole half of the tarp folded over as a roof. We can get an angled back wall to lean against and the back will probably sag enough to keep you from rolling off in your sleep.