I used a tutorial at www.onepearlbutton.com for ideas and just made sure I used the dimensions of my Kindle. I have a picture post here and will try to find it. It's actually a photo of "round 2" because, well, I forgot to sew the strap in the first one!
I used very stiff cardboard (from the cover of a 3-ring binder) inside the quilted fabric and also used the elastic straps. I'm happy with the level of protection I was able to achieve for free with materials on hand. I got a newer model of the Kindle and there weren't many "bought" covers to choose from yet.