I used ash for the runners as it was the only hardwood I had that was long enough. I planed it to the thickness of the miter slot then ripped out a bunch for this and future jigs. Baltic birch plywood scraps (that I got from a local cabinet shop that gave me permission to "dumpster dive") for the base, fence, rear brace. The fence is two layers of 3/4" ply which might have been overdoing it.
I used the 5-cut method to square the fence and nailed it after one adjustment. I added a blade guard behind the fence, and made a stop block that clamps to the fence that I'm not entirely happy with. I might have to invest in some T-track.
The only "problem" I ran into was one that I knew was going to be a problem. This sled was for my Craftsman table saw and I learned a while back by using a dial indicator that my miter slots aren't parallel. I picked the most used one and aligned the blade and fence to it. I don't recall how much the variation in alignment was. It wasn't huge, but enough to give me fits while I was aligning using the dial indicator until I figured it out. And enough to cause the runners on the sled to bind a little in their travel. It just now occurred to me that I could have used only one runner in the slot I aligned everything with
