I don't have any specific plans, so this post is more for future reference...

I've never made anything from a pattern (except a few pieces of my WIP backpack), but I'm wondering, do clothing patterns come with instructions on how to resize them, or do you buy a specific size pattern?

The idea of making a light and inexpensive wind shirt/rain jacket appeals to me, perhaps using Membrane. When you make up your mind to start a clothing project like this, what steps do you use to find a pattern you're happy with? Or is it better to reverse engineer an existing piece you like the fit of?