Well, I don't remember if the photos are still up on flickr, but the tractor is in a semi-permanent location, next to the new Coop (see my other instructable: http://www.instructables.com/id/Easy-Chicken-Coop-for-the-City-Dweller/).  The waterer has been moved into the coop for easier access, and the spot has indeed been boarded over, but if I ever choose to put it back, it's a simple matter to remove the board.  You can probably see the water fount in the photos of the coop.

The feeder hasn't moved, there's simply a second feeder in the coop.  I keep both feeders filled, and this works out well, when the girls are playing "who is top hen" games.

Don't be afraid to modify the design if you see areas of improvement!  And share those ideas here!

In my experience, they're gonna decimate it no matter what, but with something like this, at least you have a bit of control over where and how much they destroy. A lot of tractor-users will move the tractor around to let the ground "rest", but even then, the ground does take a beating. I've got the tractor set up next to a 6x8 coop in my backyard (at the end of the photoset, here: http://www.flickr.com/photos/jrossetti/sets/72157622557643038/), and after the first month of winter, I threw in a bale of straw as a toy to keep them more occupied, and it seems to help, especially when I throw a handful of scratch over the top of it.

3/4" will make it way too heavy to move around by hand. I used 3/8" plywood for everything but the inner floor. Originally the inner removeable floor was 1/2". I've made a few modifications to the tractor since then - now I've got a single piece of 3/4" plywood with linoleum for the removable floor, it adds stability for the roost, and is easier to clean. But the walls and other plywood bits still are the original 3/8".

One other change I might point out - the vinyl roofing is OK, but after having this up for a few months, I don't think the roofing will last. It's already slightly warped in some spots and while it's still keeping out the rain, it looks ugly. If you are ok with the extra weight, or don't plan on moving the tractor often/ever, you might want to consider using a metal roof. It's cheaper, more durable, and will keep the sun/heat out better in the summer; on the other hand, it's heavier.

It's pretty easily scalable, the only real problem you might have making it longer is finding redwood baseboards that are long enough if you decide to take it past 8'.

In retrospect, I could have made most of the non-supporting pieces from furring strips (1"x2") instead of the square pieces (2"x2") and saved some weight without really compromising stability or sturdiness, and this would have allowed me to make it a bit bigger too.  But also, I wanted it no wider than 3' so it will fit on the walkways in my garden better.

One other consideration, is I'll be removing the hardware cloth on the front side below the two handles with the intent of putting in another door to which I can attach a longer very portable run (probably built with furring strips and chicken wire and held to the ground with stakes through eye bolts).

Be sure to post pics of yours so we can learn from your design improvements!!

Salt Lake City, Utah - wet springs, dry summers, hot autumns, and cold and snowy winters (usually).  Right now it's 18F outside, and the chickens are huddled around the heatlamp, heh