Besides the one's posted right here on BYC, there are a number of them on YouTube.
2 chicken tractors < $100
John Suscovich - 120 broilers in Tractor
Easy DIY chicken Tractors
Suscovich tractor - sweet mods
Chicken tractor - good design - JL - Wish I could get my hands on some of that "sheeting" - our lowes/home depot don't seem to carry it...
Stoney Ridge Farmer - PVC tractor
$5 chicken tractor - Justin Rhodes AFT - Wholesome Roots
My CP hoop coops (walk-in) meant to be tractors, didn't work well on our new property. They became permanent 8x8' coop/pens w/ access to rotating paddocks or moving tractors for the birds currently in the pens.
I didn't want to hoop one and took a look at the CP & now have 2 (not quite complete) CP "A-Frame" tractors. They are 5x8', currently wired with 2x4" fencing (will be putting some 1/2" HC on it too). They are on 2x4" frames, 2 lag bolts on each end. The CP is attached to frame using fencing staples, they are strapped at top with haystring.
The gates on ends aren't done yet, so 2x4" wire is zip tied to the A-frame and just tucked behind fence staples (1 end on 1 tractor is completely strapped on using hay string, the other end on same is partially done. It will be removed when I do the gate.) The gates will be 1/2 way up the open A-frame ends and will open downwards allowing access to water & nest boxes (when ready to start laying). The top will be a solid triangle - not sure yet how I will be building it. Playing with ideas - trying to reuse things and keep it light weight.
I use tubs at the moment for watering - filled by bucket or hose. May build a water nipple bucket, not sure yet. Feed currently goes in grass - where they clean it up and scratch thru the grass. I currently have 6 chickens in each tractor -but as they mature, I really think I will need to divide it up and do no more than 4. We'll see. I could be wrong. These are chickens that will be in these permanently as breeding groups - even during the winter here in NC. I found I just couldn't free range - lost too many birds during the day while i was at work... in the 4 month period last fall/winter.
I will add pics and eventually get my coop/tractor/DLM article/pages done. The last two that I started managed to start disappeared and I just haven't re-done them...