I don't think there's anything "official" out there. Your best bet would probably be to size the 2P CP and compare it to 4P CPs that other have built or that have been used on real arcade games and come up with a dimension you think is adequate...
I never think the amount of 4P games and their level of fun is worth the extra space on the CP and the expense involved in building it... but then again I've never in my life played a 4P game with 4 people so I'm probably missing out on something... besides TMNT, X-Men, NBA Jam, The Simpsons and Gauntlet what else is there that people play?