Here is a link for a summer quilt.
http://kringlelight.wordpress.com/2011/11/15/sin50/
Couple of things...
1. It doesn't have to be as complex as that is. I ended up basically with a 6ft by 4ft square quilt with loops built into the seams along the bottom and sides of the bottom so I could cinch the bottom around my feet if I wanted to.
2. You can make it warmer, instead of using 2.5 oz climashield, upgrade to 5.0oz.
3. Basically....if you can run the sewing machine in a straight line... you can sew this stuff.
4. If you successfully do a quilt, you can do the backpack. The kits are as low as $35.
If you REALLY want the opinions of the ultralight backpacking crowd, go to backpackinglight.com. There are some serious hardcore (crazy?) ultralightweight backpackers there.