snake vivarium sizing

Question
Hello.Could you please tell me if i buy a corn snake or any non venomous snake,and at the time of buying the snake its 2 or 3 foot long so i buy a vivarium for a 2-3 foot long snake..After I buy him/her, he/she grows and comes 4-5 footlong..will i need to buy another vivarium because he/she has grown or will the 3 ft vivarium be fine?
Thank you

Answer
So sorry for the delay. The holiday have kept me off of the computer. I would just by the end of life aquarium first and not buy two. Find out the average size of the adult snake and buy and aquarium that has a perimeter equal to or greater than the size of the adult snake. For example, if you have an 8' non arboreal snake, a 3X1X3X1 aquarium would be the minimum. I always go bigger. For my cobra for example, she is about 6.5'. Her enclosure is 3x2x3x2.