I understand the main thing you talked about was the massive, massive heat problems that you see occurring. And that means the suggestion about the fiberglass roof panels on the end there, might not have seemed to make sense. I was really meaning more on the order of being able to keep them up there when temps were good for doing it, which should be at least a third of the year, maybe half.
One more thing man. If you use white poly to form yourself some walls, you can keep the full flexibility of the space you have and save a lot of money AND ensure a very high reflectivity of surfaces your light falls on, which will reduce the heat in the place ultimately. You might not want to start out with both sections being huge; and if you curtain off the room using white poly dividers you can reduce the light lost, reduce the space you temperature manage, and altogether have more flexibility.
Another thing about pulling the heat in for the lights: having had a small shed next to my house, and thinking about converting it for a grow, one thing that was on my mind the entire time, was sticking some kind of cheap, but spacious cabinet against the end of that shed, so it looked like a tool shed, but actually functioned as an (in my case) air out/filtration cabinet.
If you're concerned about vents being seen, and I would be, there's several ways around that. First, for an air-in cover, I'd screw/bolt/affix some kind of 'tool shed' item even if it was just a plywood box you built, and put some hinges onto a door in front, with a hasp and lock. This can give you a lot of space to let air in.
If you consider putting the thing inside the shed, then that same concept would give you a lot of cover and plenty of light trapping. Either way, if it were me, and I realize it's not, I'd be putting an air in concealment tool cabinet looking thinglie. You can additionally line it: with carpet or with fiberglass insulation inside for silencing.
Jackjo remember about how a real big fan, run slow, can run much, much quieter for the same air movement and amperage. A full-size squirrel cage like the one for a household evap unit could run so nearly silent if properly boxed, and it comes with a three speed motor typically. The thing about one of those is you can box it inside the grow room, paint it white for good reflection, and fasten it to that concrete floor: line the inside with insulation you glue: paper side to the wood inside - and almost totally silence it. If, on the other side of that wall, there was a tool cabinet which was also silenced the same way: the CHEAP yet EFFECTIVE way: you could pull huge air in, with near total silence. For instance, if the tool cabinet's inside, pull the air in, through it's roof: by simply cutting a huge hole in it. A few light baffles later that air could go in very quietly.
Back to the air in: if you have to pull air in for the lights, you can go one of two ways, but it's easy to fasten flex duct to a plywood box. And you can simply duct a plywood box on the floor easily. If you make the box of MDF and it's bolted to the floor the silence would be pretty golden.
Also, you could build two: one, next to the outside wall where your outside 'tool cabinet' was: for pulling in air from outside for the lights; and the other, over next to the wall facing the main building: right on the other side of wall from THAT 'tool cabinet'.
One other thing. I'm not saying take ANY of these suggestions and just go run do them with the least consideration, the least genius; but with a lot of thought for using the whole space wisely: realizing all kinds of neat stuff like the fact that if you release the heated air from the grow room that's been scrubbed up, into the roof area of the main building, - it's only a total of about - what 7,000 wats max? You could very likely get away completely fine using three of those rooftop attic ventilators, the spinning ones, and see hardly any actual temp increase down around where you'd work. Just put em up on the peak, let three of em spin around in winter, nobody'd notice. And if you released that air gently, after scrubbing, RIGHT UP at the roof level, it could be done without even coming from a detectable vent space. It would also give you some more time for mixing, and also, release it right up at the peak of the shed. Maybe it's not particularly a lot better, but it's not particularly worse, either, to release the air up high.
Something I'd do Jackjo is avoid expensive hoods, and expensive, wall partitions inside the main room. I'd look around till I found some fuggn white poly plastic and line those insides and keep it like a REAL pro would do it: FLEXIBLE and LOWEST cost with HIGHEST reflectance and washability. It shouldn't break your mind to figure out how to put a little 2X2 frame up and staple some plastic to it. That'll save thousands AND keep flexibility for future plans. Remember: the KEY to flexibility is INdecision. INdecision: DON'T COMMIT to permanence till it weighs so heavily on your mind it's pure, uncompromised genius, you eventually feel you simply cannot live without it.
Get your fans oversized: drastically oversized, and use that space you have in there to run them on low. Buy them from the furnace shop or get them free, add a 50 dollar three speed motor for each and have two double oversized fans and run them on low/medium.
Build your own boxes and go buy a masonry bit: drill some holes in the concrete floor near where you put the 'tool cabinet' intakes on the end, and also main (real) wall separating your room, and throw together fairly cheap simple mdf particle board boxes you line with batt insulation: bolt those to the floor and encase the fans and let THAT be the most permanent things you put in initially: that sort of thing.
It seems like you'd put maybe two 'tool cabinets' on that inside real wall. One, for a main, grow room intake. The other though, an air intake where you can suck in ozone that gets made with lower humidity air than that from the grow room. Mix those two in the room, let it go out the top into the upper story: creating more time for mixing: and after it travels around a little let it out, right up at the peak, back into the main part of the building; that sort of thing.
I think you should save on:
(1)interior walls: don't LINE them, don't even BUILD them at first, until you've used the whole space throughout several seasons, and you're SURE how you want it.
(2)fans & silencing
(3)specialty horizontal hoods and grow vertical
(4)wintertime growing by maybe, putting a room above where you can keep vegging plants most of spring, fall, winter, augmenting your light with sunlight through roof panels -maybe.
(5)Soil. Make your own
(6)Temperature management using the main building as a buffer against outside weather. If it's hot, blow an evaporative cooler in there when you can, and let the room intake be from low in the room. If it's cold, on your air intake 'tool cabinet' have the top be openable so your intake air, into the room, doesn't come in on the floor; indeed, you might get slick in the winter by pulling so little air out you hardly need any air in, at all. I dunno where you live.
Anyway I'm just talkin baked sorry to go on & on