I've built a couple of things.
I built a beauty dish out of a wok from IKEA. It works pretty well but it's a bit heavy to put on my cheap boom, so it doesn't get as much use as I would like. I need to start working with it more and get better with it, especially using the feathered edge of the light.
And, I built a Steampunk-styled wearable light stand. It's a backpack with two towers above my left and right shoulders, with threaded lugs on top of each tower to attach a flash with wireless receiver.
I need to build a softbox or stripbox to go over one of the lights for that rig. I've been meaning to do it for almost a year now. I have all the parts and most of my design, now I just need to figure out how to make it sturdy and secure so it doesn't blow away in a gentle breeze.