Edited to add: Due to alle the comments regarding the title of this instruction, I've changed the name to 'iron age shoes' which might be more historycally correct.
I learned to make these by using my own foot as a template. Therefore, all the measures given here are highly approximate. If your foot diverges a lot from mine (European size 39, long and narrow/slender), some sewing experience might come in handy. That said, there's no reason to be too specific in making these. As you can see, the 'laces' can be loosened or tightened to fit, and the basic idea is really very simple.
The photo here shows my own, good old shoes, made in 1997. I always use them with these thick, felted socks inside; to me, they're part of the shoe. They are soft, comfy and I simply love them. Based on my original 11 year old, several times altered, water damaged drawing, I have made a kind of template as a sort of guideline. You'll find it at the end of this tutorial. I had to scan it in two operations as it was so big, then paste the parts together on my computer, so this adds to the imperfection. You should go for the thick, black lines and not pay too much attention to the rest :)
Important: Look through all the photos before you start drawing!
Step 1: supplies
A large piece of leather, about 2,5 - 3 millimeter thick.
X-acto knife or sharp scissors.
An awl or other tool to make holes in the leather.
Pen or pencil.
A cutting board (I use a wooden one).