I built mine out of 3/16 wall 3" tubing. Just make a "T" then put another leg pointing up. Seems to me I used a 2" pipe with a 2".250 wall piece of tubing for the pivot, I don't remember the exact sizes but if you go to the steel yard just try the pieces to see what fits in what.The yard guys can usually tell you. for the mount I cut mine out of 3/8" plate. Then welded some casters on the bottom.
For high stress joints like the leg sticking up I prefer a high strenght welding process like 7018 or 6010 stick as opposed to MIG.
You can also go to the parts house and look at/measure one of theirs.