I dont know what your fish room requirements are but I always choose a 3m high wall instead of a 2.4m or 2.7m wall. With the pitch of the roof being even higher, there is a decent amount of internal ceiling space which can be used for water storage, filtration towers, general storage, shelving etc. I do need to heat my rooms in winter so the extra wall/roof height allows me to fit extra tiers of tanks for practically no extra cost. ie the cost of concrete slab, roofing etc are the same. In summer it gets too hot for me so some whirly gigs in roof or an openable roof hatch may be a good idea. A window opposite the door will also allow venturi air cooling. Some skylights for natural sun if you are breeding morning spawners but dont make these too large as algae greatly adds to maintenance. Green water is a great addition if you are on central filtration so add an extra green-water production tank outside which you can easily turn off (to culture) and on again (to feed). I dont think your room is wide enough to have multiple aisles but I would suggest adding some 100mm underfloor drainage pipe before they pour the concrete slab. These pipes might be used for water drainage or alternatively threading narrower input water pipes or electrical cables. Powerpoints and a water tap etc should also be planned for. The bakki filter (tower) is noisy but a good way to oxygenate and cool cheaply and effectively. If your filter is outside and space is not an issue then some settlement chambers and submerged bio-filter will still do a good job. Might as well add some plants to the filter too. Koi forums for pond filtration is worthwhile reading. I have set up numerous fishrooms so PM if you need any specifics.