It was pretty easy to make too. I only had maybe 30 minutes into it. If you need any help let me know Id like to see someone build one. If you go bigger you may need beefier angle 1/4" or maybe 3/8" thick and even add some gusseting. This one is about 8" across and that is 14 ga steel. I think you could get away with a 10" span before needing heavier angle.
Yes I think cones are doable as well. The angle on the swing arm handle; if you build it so you can change its angle and along with the way you feed in your stock I think cones would be no problem. It is a bit of an art not as easy as a roller. You just to need to feed in little increments at a time and take your time forming as evenly as you can. That was my first try on that piece in the picture, I had to go back over a few spots to get it round, but still amazed at how easy it was.