And I wondering what the consensus is for a bedded pack system...
Dirt floor with concrete stem wall or concrete slab?
Can't really say, but I am about to do the same. Except mine will be portable on skids. The one I will be doing will be about 8' x 12'. Am working out some of the dimensions from Woods book, as he doesn't give dimensions for one of this size. His are 10' x 16' or 6" x 10".
But I also plan on doing a dirt floor using deep litter. When it gets deep and time to move it........I'll move it.
I read your post again, and missed the part about "Long" the first time. "Long" would imply you are building attached multiples of Wood's colony house......which are multiples of the 10' wide x 16' deep units. He also gave dimensions for one that was 20' x 20', split down the middle into two 10' x 20' units. Not sure how "large" your large flock is going to be, but those were used for up to 40 to 50 birds per module.
Back then (100 years ago), Woods and at least one contemporary of his firmly advocated away from dirt floors in favor of elevated concrete slab floors inside stem walls in these larger permanent barns if you could afford it. By elevated, it meant the bottom of the slab would be no lower than the grade of the adjacent soil outside it. The top of the slab elevated above it.......so the inside slab would not be wet from ground water sources. Top of the stem wall above that at least as deep as the level of the litter......and then some. The concern was mostly damp, wet litter on dirt floors, plus ability to clean them, soil contamination over time with the high N droppings, and rats. About the only predators either of them mentioned on a regular basis was hawks and rats. The rats building tunnels under the litter and coming out to snag baby chicks. But again concrete, with a shallow layer of litter on top, which they wanted to keep really, really dry.
But the worm turns and now the trend is to deep litter. In his book and websits, modern guru Harvey Ussery now advocates deep litter over dirt floors. But Harvey and others who follow his suggestions may not be keeping as many birds as you plan to....either in total numbers or density per SF, and his climate in Virginia may be milder. His deep litter is a cold compost pile up to a foot deep, but he has a large garden and can use a lot of compost. If you plan to have that many birds, hopefully you have a plan for that much spent litter too, and maybe a way to get it out of your barn that does not involve a pitchfork exclusively? Back then, on the Long houses, there was talk of overhead trolley tracks that ran down the length of the multiple Long colony buildings. Anything like a front end loader on a small tractor or skid steer was a fantasy they could only dream of and likely would have given a left body part to get.
But even for the portable units like I plan to build, they both advocated for elevated wood plank floors. They wanted their buildings well ventilated.......and dry. Since mine will be portable, and since I intend to keep only 6 or so adult birds at a low density to start with, I'm going to try dirt floors, but with the ability to go back and install a wood floor if deep litter over dirt does not pan out. My concern is moisture rising up from the floor and dampness.......even with all the ventilation. My guess is the colder your climate, the drier (and more ventilated) you want your building?
On the wet concrete floor, if you put down a layer of gravel beneath the concrete slab.....it does several things. It beds the pad......more of a cushion beneath the pad so soil movement doesn't affect it.......it also acts as a drainage bed to keep moisture beneath the pad from wicking up (and especially so if you put down a vapor barrier between the gravel bed and slab.....basically just 6 mil plastic film).....and elevates the pad so about the only moisture on it will come from above.....either from rain and snow from any open windows or from the birds themselves. This is how they built a "dry" house. If you were really concerned about ground moisture wicking up, you could even put in tile drains around the footings to drain any water away from beneath the slab. Do that and it should remain bone dry. To get the litter to compost on that you might have to add water to wet it down.
As near as I can tell, one structural issue to overcome with a Woods house is support of that monitor roof. The wider the building, the larger the problem becomes. I seem to recall some passage where Woods mentioned one of his barns had sagged in the middle, so needed a support post. One way to overcome that would be to use a wood truss in that area. Basically the same type of floor truss that home builders would use to support a too long floor span.
That might leave you screwed on using transom windows, but this is a chicken house. For windows, we might be able to use clear corrugated plastic nailed to a frame. The downside is the truss verticals and diagonals might be visible through the windows, and perhaps subject to weathering and sunlight. They may also make those manufactured I-beam joists down to the 6 inch level. That would do it too, and might help with any side racking. Still pondering these options.