I thought about making a down quilt. And when I started reading directions that included zipping myself in a tent before opening the bag the down came in, I realized that I would not be able to control the down well in my environment, and did not want to waste material that costs 20-30 per oz.

I suspect that the sleeping bag mfrs are able to afford machinery or a controlled environment to better control the down and make it much easier to quickly assemble down bags with minimal waste. You might check into that before deciding you can make a cheap quality product - what is your time and temper worth? I decided my time was worth more than the $240 I spent on my down quilt. After first making a synthetic quilt, which is far easier, that made the most sense to me.
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"In the beginner's mind there are many possibilities. In the expert's mind there are few." Shunryu Suzuki

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