I like this one. I downloaded it so I could refer to it. When you get to my age, one tends to forget easily.
I have made several from this tute, adding a zippered inside pocket, and modifying slip pocket for phone, keys etc. I found Bobby easy to understand and think she did a great job on her video. Once your comfortable with this bag, you will modify it as you go along I'm sure. Good luck!
https://www.youtube.com/watch?v=h00B8af3xNc