I made all of mine from a variety of wires I had on hand. Some are bare copper wire, others are insulated. I don't really have a preference. The insulated ones maybe grip the wrenches better. The copper ones look cooler, I think.
My drawer is currently a little disorganized because I've flat run out of room (it's the thin, full-width drawer in the HF 5 drawer red tool cart). I'm currently storing 84 wrenches in that space, and it would be totally fine except for the two big guys in the front taking up a tad too much space. My point is that you can do a lot with a little when you use springs to organize your wrenches.
Here's a photo of my drawer last year, before I added a number of wrenches. It shows what I was doing with some of the smaller sized wrenches.