...most of the ones I've built over the years use a couple of PVC pipe lengths, spaced out so the bars rest on them evenly.
I built one for the co-op here that had multiple tiers, and was bolted to one of the storage cabinet tops, at about eye level.

Here's the one I use currently. If you want to store a lot of steel handlebars, this is not a good system, because the weight quickly overwhelms the PVC.