I made this one to accommodate my "custom" panniers. This was my dog's backpack from about 15 years ago. I cut off the straps to use it on my bike. However, the area between the bags is narrower than most racks. A Dremel tool, rivet puller and about $6 in supplies from Home Depot got me rolling.

The rack is built with supports and brackets from a cheap rack that I pulled from an LBS dumpster. I used aluminum angles for everything else.