This is the simplest leg warmer pattern I could think of. It needs no shaping at all just a large piece joined at the sides to make it round. I made a crochet band and some little pom poms to make ties to keep them up. you could make an i cord if you know how to. Last winter when it snowed I wore mine under my jeans or inside my willies to keep my legs warm.
Pattern
Cast on about 80- 90 stitches on 8-10mm needles (depends on the yarn etc) and work in a 2x2 rib continue to work the rib until the leg warmer has reached desired length. These are about 10in long