I finished the lid and it works. I used an old tank divider and cut it to fit. THe tank's sides all measure 10 inches with the exception of the height which measures 12 inches.
I left an extra inch or so on all sides (to help prevent the lid from falling in the tank) except the back. For the back I cut off an extra inch to make room for wires and the mount where the filter/light attaches to the tank.
I cut out a five inch by five inch square for the filter/light. The filter/light is smaller than that but the extra space allows the water to flow from the filter correctly (you will see what I mean in the pics).
I want to thank you for your story. I have a fluval chi on my desk with a 1/2 moon king betta. I just built a cover using egg crate. I might but some fake ferns on top as well.
Sorry for your loss.
Clay