Cut every piece that you need...
the big one 3 times
All together, instead the leather you can use some regular fabric you want
I made a nice embroidered line on the leather.
Pin the fabric together and sew
watch out!! try to get the half circle as an little bit smaller as your piece of leather. When you did, sew the leather on it with an other ebroidery stich
sew the back site on the bag inside out
The lining, I made a small pocket for it.
sew both sides inside out on each other
The closure. sew together, put inside out, and stitch
sew it on the back site of your bag
Put the inside in the outside
Close it with a piece of bias band or make one with fabric as i did
And finaly the straps, then you are done. I hope you will enjoy it