if you want a big one , you are talking micro marulia ( req, min 6ft x 3ft x 2ft ) for single fish, maruloids or straita or diplogramma or barca ( min 6ft x 2.5ft x 2ft ) for a single fish .
the main dimension for life is the front to back measurment , the tank should be at least the the same width as the fish is long and micro and marulia (the two biggest) will reach 3ft in aquaria , the others mentioned will all reach 2.5ft in aquaria and have the potential to reach 3ft.
if you wanted a few micros ( the big mean ones ) then you would req something along the lines of 10ft x 4ft x 4ft
cheers col