I have used the one, becaused I got one, from Agritek Industries and have been very happy with it....It is well built and work as they say it should I can tell you that much.
I looked at possibly making my own as suggested by L3650 but with the cost of all the steel, the labor involved not to mention the time involved, it made that option very impractible so I called and ordered one up. Shipping costs were reasonable, they offered a money back guarantee and I got it in 1 day!