Funny you should mention it, I started working on some this weekend. I had a couple of projects to do and went to my buddy's shop to use his MIG machine. I didn't get around to much on these besides design as fabrication on a few other projects took so long. I'm going to try to finish later in mid-June.
Here's what I'm thinking: 2"x2" square tubes with 0. 25" wall thickness for the bars and mounts. The mounts will be welded to 0. 25" plates that bolt to the frame. The bolts will go through crush sleeves/bushings that will be welded to either the back side of the plates or into the frame. Yes, these will be very heavy and labor intensive. Besides cab protection, the main design goal is to be able to lift the front wheels with a Hi-lift. If off-roading is important to you, I think you should use heavy material as alot of the production stuff can easily bend and the nerf bar will be what pushes up and into your sheet metal. I've been told to hold the bars at least 2" from the cab as there is that much flex in the body mounts. Good luck.