"Just google 'sleeping bag pattern' and there's tons of links like this "

You just googled a link from this very website. Look at the left of the page for a link to the "make your own" home page.
Make a liner bag first. Its a very simple project but you will learn a lot. Have a great deal of patience with the bag. Sleeping bags are probably one of the more advanced projects. I would even say complicated backpacks are easier to make (smaller). Start with stuff sacks and such until you get comfortable.
Scott