Big!
Why don't you google his adult size, put double that for length and close to that for width and 4 inches above that for heighth..that'll give you just a simple estimate...not counting tank mates or decoration or internal filters..... they need caves.
For any larger fish active do just that. An dthen run numbers by the keepers.
I don't think your parenmts wiol allow you that big atank..
I am making a 170 for my wee Black Ghost knife that is now going to expand befoer it gets made so I can make it a biotope.