So far I've made myself a 9x5 tarp, a Henry Shires style tarp tent, and a backpack. I am contemplating moving on to trying some clothing items now that my skills have improved. However, I feel this is a different realm which may be much more difficult. What I would like to make is some sort of insulated vest. Here are my questions...

What type of insulation should i use?
What type of outer material? (assuming some sort of non-calendared ripstop, unless down) (If down, how much?)
Anyone have a pattern?
Am I in over my head?

I am curious to see/hear about what outdoor clothing items you guys have made!