I had one of the racks like in moresound's second post, here. Never really loved it. I mean, it was okay, just nothing spectacular. Got it free, sold it for $30- 12-space rack rails cost about $12 each, so when the one person who responded to my post asked if I'd take less, I said no- I figured I wanted to get enough to cover the cost of replacement rack rails if I ever needed some.
If you build your own, arca, you would really want to make it more sturdy than the one moresound showed. Once you get the angle right, you won't need to change it, so I would built it out of plywood or such.