I purchased a little helicopter and kept running into the walls, bending the blades. So I sat down, learned OpenScad and made the shroud.
-- update (4/7/13) --
Added a version which trims down the weight. I have not printed it yet but give it a shot!
Print and try it on for fit. If it does not work update the parameters at the top of the .scad file and try again. It took me a few tries to get it right.