Well, first of all let me state that the frog you're looking at is most likely Allen's slippery frog, Conraua alleni and definitely not Conraua goliath. Alleni is often sold under the name of goliath frog. That being said, I believe the husbandry and cage size would be very similar to the American bullfrog, Lithobates catesbeianus. In other words, a large semi-aquatic set-up. Guessing, I would say a minimum of 40 gallons, but bigger would definitely be better.