why not use it for fish and set up a $10 rubbermaid for your snake? it'll hold the humidity better, temps will be easier to keep constant and your snake will feel more comfy in a rubbermaid/sterilite than in a glass tank.

that said,... if you wanna use it for a snake... yes you need to replace the lid. i would use melamine myself.

i use ceramic dog dishes for water dishes so the snake can't knock them over.

hide boxes can be made out of many different things or you can buy one from the petstore. it's totally up to you, just make them nice and snug so your snake feels safe in them. having them both identical is a good idea as well.

i have no idea how you would make shelves...

i think you could definitely make it look cool... just remember that you need to be able to get into it and clean - so don't make the shelves permanent as it may be hard to clean if you can't take them out.

hope my suggestions help ya.
aleesha