I was going to build one, and I went to a local Rainbow Direct Factory store to purchase the hardware from them. They use some very well designed ones IMHO but the lead person at the store told me they do not sell the parts. They only sell replacements for an existing unit. I did not push the issue. I honestly thought that was poor sales, I am not going to buy a entire unit why not make a few hundred in hardware.
I am with Jim, once I weighted the expense and time of building one we decided that we are getting ours from Samsclub. Have to wait til we move into the new house but for $1k it is really a pretty good deal for what you get. Check it out.
http://graphics.samsclub.com/images/...1360061_L4.jpg
Greg