I fully agree with Don's points above.
A few other configurations to consider:
- Paper tubes (especially if of several layers glued together) can hold a decent compressional load. Look at a paper towel or shipping tube for some ideas how to make this work.
- Unless it's in the rules, don't limit yourself to having one of the bars be horizontal. Also play with some acute triangles (compression at the bottom, tension on top). I suspect that for a given amount of material, something close to an equilateral triangle or a right isosceles triangle (with the right angle away from the wall) will give the best results; both members will contribute a force in the vertical direction.
- To make a tension member from paper, you don't need a large area of coverage, but you do need to ensure that tears don't propagate. A time-honored technique of making fiber materials stronger under tension is to twist - think of a rope or cable.
Out of curiosity and for my own possible tinkering someday, how far out does the cantilever point have to be, and how much weight is it expected to hold?