We have made two tops for the couple of aquariums we're still using. Both take the place of the screen tops that were on the aquarium. They are much easier to use, more secure and look so much nicer.

I'd love to see pictures of the tank you built. That's my next project.

We got our Plexiglass at Tap Plastics. Great people to deal with, if you happen to have one of the stores in your city. Otherwise, just look around for a shop that makes stuff out of it and I bet they can cut you pieces.