This model is pretty much to scale, so if printed too small, it will likely end up with spiderweb wings. This was printed on a Form 2 by a friend, so I'd recommend modifying the file yourself to thicken the wings if your printer just wont do it.
Methodology
I used Blender to model this aircraft. I take a minimalist approach to modeling. I attempt to use as few vertices as possible and use a tool in blender to do the smoothing out of shapes for me. The end result is a mesh that's as accurate as I can get it and still maintain printability. The F-117 is obviously very geometric so it doesn't necessarily require an extreme amount of work to shape it out using line drawings.