As long as you have appropriate heating and plenty of hides/grund cover, I'd say the bigger the better.
One of my vivs is four feet wide and three feet tall, with a couple of shelves. Corns that have used it seem to be fine in it.
My only warning is that the elaborate design can be wasted if you end up with a non-climber or one that prefers burrowing. I have a few, so I've just tried to fit the active climbing Corn to the enclosure, which has worked well. Maybe wait and see how yours turns out aged around three, before planning a glorious showhome that he'll never use!