I finally just built a larger tractor for our layers, I had done a small one first to kind of get a feel and learn some lesson. Well I learned more lessons on the second. New run is roughly 5x10x4ft high, coop is actually a separate piece and the adjoining wall is plywood, there is a hinged door on the run to block the coop and the coop has a drop door, so I can lock them in either when I separate to move
Almost immediately after building the larger tractor I regretted doing an inset door, for my access to the run. The first time I moved it from the garage the natural unevenness of the yard lightly bound up the door when the opening went out of square. I might go back and do a door that rests against the surface, that wouldn't be affected by the tractor frame twisting on uneven ground.
I just put the chickens in the new tractor today and just let them have free run of the whole thing, in hindsight I should have locked them in the coop at least overnight. I went out just after dark to find them in a pile in the run, so I had to go in to move them to the coop, well I didn't have a way to latch the door from inside. Found a bungy cord and managed, but tomorrow I will put a latch on the inside.
Sofar I would say use surface mount doors they are more forgiving.
If the coop or run are large enough for you to enter make sure you have a way to keep the door closed behind you.
It is easy as a well placed screw but I also ran screws in next to the latches to hang the carabiner clips on when I am working with the door open. On the small tractor I always held onto them or set them down, dropped them etc. one time even failed to latch a door and had some escapees. with the clips hanging next to the latch I don't have to hang onto them and they are hard to forget to put on. I have real racoon concerns, hence carabiner clips on lockable latches.
I know some of that is simple and little but I would rather have done it first than stress out the hens with drills and screw guns while they are in the coop I am working on.
Oh one more lesson I learned from the small tractor. Make them so you can do everything from 1 or 2 sides. I had the drop rood to the coop on the opposite side from my access door to the run and what that meant was when I moved the tractor and them went around the other side to reopen the drop door, I either had to move the coop an extra couple feet or walk in poop.