Not for beginners. This is an intermediate to advanced tutorial where you will learn a technique that I love to use on my briefcases, a double gusset. This technique can be applied to handbags, briefcases, pouches, card wallets, and anything requiring two separate compartments. Once you master this technique, just follow the same steps to make any size double gusset project you desire.
 
Print out the PDF templates, glue them to some card stock, and work your way through the written tutorial. 
I've used a code system where an instruction is written in the notes, and it has a corresponding code that is marked on the template to help you visualise what I'm talking about, in case you don't understand some terminology.
What you will need-
Card stock (1mm or so) to glue the paper template to. (Do not scale when printing)
Veg tan leather- 2.0mm-2.5mm for the main panels and flap, 1.2mm-1.5mm for the gussets (1.2mm better). Strap leather 20mm wide, 2mm thick or so.
All of your standard tools, knife, pricking irons, glue etc. Round awl, pins or harness needles will be used to line up gussets. No skiving required in this tutorial.
Hardware- you can use snaps, tuck locks, Sam Browne studs or a buckle and strap to close the pouch. Up to you. The shoulder strap will need a buckle for adjustments too.
Time and patience- It's got a bit of work in it even though its a small pouch. Take care when gluing in the gussets. It's the most technical part, and needs the most attention.
 
This tutorial teaches you a construction method you may or may not be familiar with. It is not about the small details like stitch spacing or thread size. I will leave that up to you. I am assuming you know how to cut leather perfectly from a template, mark stitch holes on any length edge, saddle stitch, edge crease and burnish. If you aren't confident in these skills you will still be able to do the tutorial, but it may take longer.
You can choose your own locking or closure method, but I have provided some guidance to what would work well. 
If you have any questions during your build, feel free to email me at martin@carswellleathergoods.com