This is my version of messenger bag with flap from an old pair of jeans that you can find all over the internet. Most versions did it without flap, so they looked like tote bags with longer straps.
I forgot to take the pictures when I made this so I couldn’t show you how to do it step by step, but I’m sure you could find it on the internet.
It took a while for me to finish this project because I sew it all by hand. If you use sewing machine you could do it alot faster. But make sure that you sew the bottom part twice or double to make sure it wont rip by the weight of the stuff you put on the bag.