In reply to mwr72:
Making a 'stitch through' down jacket isn't rocket science (but don't try for a box-wall or other baffle style, because that's way harder to design and engineer). It can be as simple as getting a couple of windshirts, sticking one inside the other and sewing them together whilst stuffing the space between them with down. How good the end result will be compared to buying cheap off-the-shelf gear though... I don't know
I looked into this a little while back, and decided that the amount of time and effort required meant that buying something ready made was more economical. YMMV.
Fill:
http://ukhammocks.co.uk/shop/article_38/850%2B%28EU-cui%29%E2%80%93Down.htm...
You can get complete kits, but only from the states so postage and customs may well make it uneconomical:
http://thru-hiker.com/kits/whitney_kit.php possibly you could get the plans alone from them and get materials fdrom this side of the atlantic....
www.extremtextil.de look good for the shell, because they explicitly state that some of their stuff is downproof:
http://www.extremtextil.de/catalog/Ripstop-Nylon-downproof-ultralight-10den... and they'll sell you down and other bits of stuff, too.
profabrics/pointnorth are UK based, but say a bit less about their gear. Seems to be an excellent range though.
http://www.profabrics.co.uk/shop.php
Doubtless there are other sources, but you'll need to search. US forums are possibly the best place to search for more advice... search for magic words like 'myog' (make your own gear) on backpackinglight.com, for example.
Good luck!