How large a cage is does not matter, Remember, outside, there is no walls. Just for kicks, last night we found the first hatchling of the year here. A tiny longnose snake, it was crossing a road about 30 meters wide.
The key is, make sure the lid on the take is covered or solid, and plenty of areas for the snake to hide. Also one trick is, put all the stuff that's in the snakes cage now, in the new tank, so it recognizes its scent. Best wishes