handmade waterproof footmuff need pattern please

[bacon]

I have now found the perfect 100% waterproof fabric as most purchased ones are only showerproof. I'm going to make one up but wondered if anyone has come across a cutting pattern. My son is nearly two and hates the clear waterproof cover that goes over the top of the pushchair. I need a good foot cover but not willing to spend silly money.

Anyone?

If you have a footmuff already could you use that as a template?

I'm not an experienced seamstress, but for a shape as simple as a footmuff I don't think you'd need to take the original apart, you could just estimate the overlap for hemming/seams.