i wouldnt build just one tank...id build a proper aquarium with many many tanks of diffrent sizes so i can have lots of species tanks. i mean if money were no option...i dont think i would be happy with just one tank hehe
my big tank is 8x2x2 but if money and space would permit i'd love an 8x8x8.
i went to the steinhart aquarium today and saw alot of the same fish all of us keep in these huge bedroom sized tanks and it was amazing. the true potential our fish under the right conditions is awsome. i took a bunch of pictures while i drooled. i'll post the good ones when i get a chance.
I webnt from a 10 to a 55 to a 75... i got smokin' deals on all of them... i got the 75g for 150$ canadian, with under gravel filters, and another filter, the power head and stand with 2 heaters all included... it was partially used, but the stuff that was used i cleaned up and repainted the stand, and now it's mint....
The best size is a lake. If buying that is out of limits. Then buy the longest tank you can afford money and space-wise. Last put in the minimum fish you would be happy to watch.