Hey Zem ... I myself have spent a few hours in my head working out such a grow room......

What i came up with is this... Temp control is the biggest issue as you said above... my solution is this..

rent an irrigation machine from a rental place and put a series of loops under the ground in a nearby feild with the standard irrigation tubeing they sell at home improvement places.

Connect to a hot water circ pump they use for boilers.

Add a thermastat.

Then connect them to a coil for heat transfer. this can be made by soldering baseboard heating tubes together in a series.

put this coil on the air intake to the rooms to lower the entrance air temp..

You can also plant some sort of ground cover over the "cooling" field like strawberries.
This will help the water in the loops to cool faster and be cooler.

Please keep in mind that i personally have no idea if this will actually work or not... but i would bet money on it...
The best of it is that you can do it as many time as you like..you can have coils within each room that only recirc the air inside that room. All that cooling right from the ground...

Good luck man,