I made this bag for my violinist friend Theresa who wanted a long shoulder strap. You could wear it cross body. The zipper panel is a little tricky at first but the video below explains all.
I used this video to learn how to make the adjustable strap. Start at 11:40
I used the video below for the bag construction except I placed the strap on the outside edges rather than having two straps as in the Zippered Hand Bag.