Too simple to be called a pattern, really. Excruciatingly simple. Any sock yarn will do.
Which needle size you use depends on how wide you want the leggings to be. You could also, of course, make the leggings bigger by increasing the number of stitches in the initial cast-on. Your call. After all, it’s just a tube.
2009-08-30: New version of PDF uploaded; all changes are purely cosmetic.