Here are a couple patterns if someone want to try to make one totally from scratch: from Urban Threads, and from Chica and Jo.
I remembered that I had this little portfolio notebook thing, that happened to be the exact size for my nook. I think I got this at Goodwill for less than a dollar. Its just a cheap notebook holder from some company. So check your local thrift store, or maybe you have a freebie from some company lying around!
To change it into a Nook holder, I sewed elastic onto the corners of one side. It was a little bit flimsy, so I inserted an extra layer of thick card stock in the pockets on each side. The card on the left side was sticking out a bit, so I covered it with fabric. I also glued on a piece of scrapbook paper over the little pocket that had a company's name on it. Then I sewed a little strap with a snap on the end on one side, with the other side of the snap on the top of the cover.
Outside top view were the snap is attached:
Outside back view where the strap is sewed on, and if you look really closely you can see the little lines where the elastic was sewn:
All ready to go with my Nook!