I made this really simple bag out of 1.8mm thick leather. It can hold my 10" tablet along with my books.

This is the first time I made a bag so be sure to read the "notes on the build" section before trying something similar because I will explain some of the things I don't like or would do differently.

Supplies

1.8mm thick piece of leather (I used two color so I had two skins but you can make it with one) roughly 50x100cm
A cutter
2 needles
1mm waxed and braided polyester thread
Round stitching chisels
two zipper (60 & 20 cm long)
Edge Skiver

Step 1: Designing & Cutting the Pieces

I didn't make a precise pattern. I displayed some of my school books on a piece of paper and added some space around. The front and back are 34x25cm with 2cm radius corners and then I figured out the outside perimeter with a 6cm wide piece of paper that will be the outline. The handles are approximately 26x2cm.

I punched the stitching holes at the same time I cut the pieces as it was quicker. All my stitching lines are made 5mm away from the edges.

I made a reference hole in the middle of all the stitching lines so that every pieces would had aligned holes.

I decided at the last moment to add a brown side pocket. That's why it isn't in the pictures.

Step 2: Preparing the Zippers

For the upper zipper I used pieces of leather that I thinned first and rolled the edges so they look better. Then it's just gluing and stitching them. I cut the whole length a bit longer than I needed because I didn't know how long I exactly needed it yet. I cut the excess after measuring the outside perimeter.

For the side pocket it was really easy I cut a 20x2cm hole on the piece and stitched the zipper in place.

Step 3: Preparing the Handles

The handles are really the simplest one I could think of and preparing them was fairly easy. I just glued one side and then the other one over it and made a stitch roughly in the middle. The pictures speak for themselves but if you need more details ask them in the comments.

When waiting for the glue to dry I put some heavy books on it to keep the piece as flat as possible.

Step 4: Stitching All the Parts Together

I stitched the bag "inside out" and then reversed it.

I added D-rings on the sides in case I want to add a shoulder strap in the future.

Step 5: Notes on the Build

Overall I am happy with the result but there are things I will try to improve.

The outline is not as "flat" as I wanted. By stitching it from inside it keeps it more round. Maybe this leather is too thick for a bag that is that small.
The way I made the handles doesn't look good at all when you look at their base.

If you have any idea on how to improve it I would gladly read about it in the comments.