I would recommend that you make your cage 79" x 30" x 18". That gives you the biggest bang for your buck. You can make your cage out of EXACTLY two sheets of melamine without wasting any.

I believe that plywood cages that are caulked and painted are a better choice than melamine. If your melamine becomes damages it is quick to absorb moisture and whatever disgustingness comes out of your snake to provide that moisture LOL.