There's no step by step for this one, I'm just sharing to give ideas.
Here's how I made my bag:
I cut a cardboard according to the size I want for the side of my bag and put the pieces together which helps seeing how it will look like when it's finished. For this one there's just one piece of blue jeans (you might not need the cardboard for this one).
What I upcycled:
* 1 old blue jeans
* a pink jeans skirt with white flowers
* shiny bands I cut off an old t-shirt
* black jeans from which I cut out the handles
What I bought:
* some grey thick fabric for the lining
* some black skai For the bottom of the bag.
Dimensions for the bag.
For the big rectangles ( blue jeans side): 34 x 32 cm + 2 more for lining fabric
For the smaller rectangles (pink and grey side ): 32 x 20 cm + 2 more for lining fabric
For the bottom: 34 x 20 cm (of skai)