No matter which way you go, purchasing a pre-made cover or making your own, you'll need to lock it onto your aquarium. Octopuses are much stronger than you'd think and could possibly push an unsecured cover up to squeeze under it. We have chosen to make ours. Lexan is my 1st choice for durability non-warping. It is more expensive but tough stuff. It will even hold up under a 250 metal halide. Plexiglas works if you add braces otherwise it will warp. We made an access door in the center w/screw down lock. On my 120 due to the cross bracing we made 2 separate covers. We fabricated a sliding screw down lock. I personally would stay away from glass. I have had glass covers in the past and find they chip too easily. Remember you will be opening the cover daily for feeding. Let me if you want photos.
