Re: Anyone make their own jackets etc.
Like Chuck said, Stay away from the top of the line mega stuff. Unless you are a circumnavigator that spends weeks on end in the Southern Ocean, chances are you don't need it. You can get good quality "Coastal" gear in around the $120.00 range; Gill, Henry Loyd, and others. Shop when the local boat show comes to town, this is where you are most likely to find the best deals.
I am not sure even a good seamstress could duplicate all the features you find on the stuff. The inner sleeve with the separate velcro enclosure at the wrist is the first thing that came to mind. I can't imagine how the DYI could duplicate that, than again, I don't sew. Don't forget breathable fabrics, zippers on every pocket, inner pockets that are lined. There are several things I would think you would be hard pressed to duplicate.
Courtney is My Hero
If a man is to be obsessed by something, I suppose a boat is as good as anything, perhaps a bit better than most - E.B. White