>>Lowes has pieces of 3/4" Pine board in sizes 24" wide by 24" up to 72" long.
That is edge-glued pine. Sometimes called laminated pine. It is basically a series of pine strips that are glued together. I build a small bookshelf for my girlfriend from this material and it was easy to work with and looks nice. Now it holds some plants outside and has been rained on all summer. Remarkably, it has still held up. I'm quite confident it will work great for a snake cage. but it will need to be sealed and when you seal it the laminates really show up. It is not the most natural look for a snake cage. Definately attractive, but just a different look.
>> ...so I'd like something big enough so that I don't need another cage.
Nothing wrong with building a larger cage. Heating and humidity can be more difficult but it's certainly still possible. Personally I would stick with a 2'x4' floor area simply because lumber tends to come in 4' increments and I hate wasting wood. Also it makes it easier to have the grain oriented vertically in a tall cage, something I prefer.
>>So If I can use it I would like to and stay away from Plywood because I'd like it to look nice in my livingroom.
Umhh, some very high quality cabinets are made from plywood. I have made a handful of very attractive cages from laminated plywood.
Here is one that I made originally for a friend's Jungle Carpet Python. It is made from cheap oak-laminated plywood.

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Current snakes:
1.1 Gonyosoma oxycephala - (Silver/Yellow)
3.4 Gonyosoma oxycephala - (Green)
2.1 Gonyosoma janseni - (Black)