Hello Oliver and welcome to FF! First thing to do is read this excellent Care Article: Frog Forum - Pacman and Horned Frogs - Ceratophrys - Care and Breeding. There you will learn how to set-up a proper enclosure for a Pacman.

Most adults will be happy on a 10 gal. tank since Pacmans are "sit and wait" ambush predators and don't move much. If getting a baby, that size tank will actually stress it out. One of those plastic keepers like the ExoTerra small Breeding Box is a much better choice until frog is 2 in. from snout to vent (SVL). Since controlling temperature and humidity is easier in the 10G (and you will need it in a couple months); a good trick is to set-up the 10 and place the smaller critter keeper inside it until it's time to release frog in the larger tank. Good luck !