Take the architect and the tank designer out for a drink!
Really these two people need to be on the same page throughout the design as the tank will form a considerable part of the structure. It will have an effect on the house design from the first page.
I'm glad you haven't been dissuaded from this endeavour as yet!
Assuming you use concrete as per your initial outline,
The concrete alone will cost you a few grand plus wages, concrete prices fluctuate, also delivery distance plays a big part on price, if you are isolated (outside of a delivery perimeter) it will cost more. (Concrete spec will also vary in price, a harder mix costs more)
3-4 men should easily cope with the shuttering/rebar and pouring. (Ideally one man needs digger exp. or that's more money on a driver. (Excavate at foundation stage to keep digger hire cost minimal)
Any good building team will be able to work to the drawings provided by the tank designer, after all that's the way it works in the real world!
I'm not sure a regular architect could engineer this tank. Your building team could (would need to) work the job in alongside the main build.
I DIY on my days off but a build like this I would surely like to be a part of, it ticks all of my favourite boxes, construction, engineering and fishes, and this is 20 times the size of my biggest build, I used concrete and steel for a stand. I moved the tank once with no issues except my biceps! Yours will be permanent, even if you change your mind.
If I was in a position to consider something like this for myself I would set aside 5 grand to get to this point, then you still need viewing panel, tank lining and system equipment and associated plumbing. That gets you a basic system, now factor in substrate/rocks/stock.
15-20grand, that's my rough guess and so for me, it will remain a dream!
Your tank will be the size of my fish house. (You can buy all glass tanks that size but the water is around 1 meter deep, that could work out much cheaper!)
My LFS has a custom 3meter square tank by 1.2 depth, it holds over 9000 litres.
It's only half what you want but maybe the DIY glass option could be more cost effective. (I say DIY I mean built on site, same thing to me)
Do you have a specific shape in mind or is it just a numbers build?
3x3x2.2 or 6x3x1.1 or 12x1.5x1.1 meters it's all the same volume. The deeper it is the better the glass spec. will need to be, this will increase cost.
12-meter long glass fins for the new entrance - Van Gogh Museum
Anything is possible in glass.
