The first thing I'd need was a good piece of leather. I quickly found out there are a lot of variations. There are differences in tanning, thickness, stiffness, color, etc. From what I could tell I'd need a piece that was 4-6 ounces in weight (that's really thickness), semi-soft or soft, and oil-tanned. The color was just preference. I found that The Leather Guy sold what I needed at a good price. I bought a piece that made two large journals and one small one for around $30.00 (http://www.theleatherguy.org/leather-hides/project-pieces/oil-tanned-pieces/).
I knew that I'd want my journal to be refillable. That way, when I was done, I could continue to use the same journal without having to make a new one. The best technique I found for that was on YouTube here - https://www.youtube.com/watch?v=Yju82AwTb_M. I adapted his technique to what I wanted. I did not want an elastic tie around my journal. I just used the elastic for the spine to hold the paper in.