Well, think about anchor points and draping - the purple sweater parts on the top would anchor it to the under-boot - or even just to the pants.
You could even just sew them to the pants.
I'm not sure how you could do this without attaching it to a pair of shoes - the metal-like bits on the bottom of the shoe are going to be hard to do without attaching them to a stable structure underneath. I think it would be best to sacrifice a pair of shoes / boots. They don't have to be very tall since the boot cover can do most of the work.
As for the pattern itself, think about how the shape would look if you laid it flat. You can always use some muslin and pin it and pinch and dart and draw on it and such if you don't have a lot of experience with making patterns yet. Have you ever drafted a pattern or something like a body block before ?
Disclaimer : This post written by a Grumpy Old Man
Actually in the pipes:
- Remaking Ser Loras doublet.
- Luke Skywalker, A New Hope
- Wind Waker starter costume in swim material
Eventually: Paul from Dune, Faramir, Harry Sullivan