When designing & building a fish house, or fish room, you have to pretty much reverse engineer it. You have to figure out what you expect out of the finished product. Keeping different fish requires different tanks, heat, filtration, and water conditions. Breeding setups require different configurations from fishkeeping setups. Insulation, heating, cooling, and ventilation all depend on the climate in your area, and the fish being kept.
If you post your general location, as well as what you expect out of the fish house, you are bound to get more help. A setup orientated towards keeping a vast collection of various corys has different requirements than one breeding large cichlids, such as oscars.