This is a project I'm planning on doing sometime too. I'm thinking of using 1-inch lumber, probably 10" for the sides so that it will cover the black border. I've read it's good to paint the inside with a sealer so the lumber isn't absorbing the moisture from the tank. A real simple way would be to use plywood, but if you're going to DIY there are endless ways you can design it considering filters, tubes, and cords in the back and access from the top. With a DIY project like this, think about what you want and then think of a way to fit it together. Good luck!