Hi TM,
I would like to give you a couple of hints for building a Fishroom.
When I build mine, which is 2.2 X 4.5 metre square (Just under 10m2 and therefore no permit required) I installed water, floor drain and floor solar heating. It has a termostat regulated wall heater keeping the temperature between 24C and 25C, it is well insulated with 100mm batch in both walls and roof, I also have a small air compressor.
There are tanks measuring 150 X 150 X 300mm and 150 X 300 X 300mm on both side of the room, and a few tanks measuring 300 X 300 X 600mm.
I collect rain water from the roof in a big plastic drum outside, from where it is pumped inside the fish room filtered and kept in 60 liter tanks where it sits untill the room temperature brings it up to 24C.
The fish room is now four years old, and I have found it to work very well for breeding several species of killifish.
In the event you need further details or information, please feel free to contact me.