What follows is just a description of how I made mine. I used a lot of scrap I had around the house and fudged it in quite a bit. Your results may vary. And lets get this out of the way. I use a hydraulic Jack with mine and it exerts 10 tons of pressure... should things get out of hand with some over amped jack operator I take NO responsibility.
Step 1: Make a frame
I screwed them together as I went so I did not have to wrangle them into position later.