I just made a screen top. I build a lot of stuff so of all difficulty levels but this is really easy so no matter what your experience you can do this.
Go to the Aquarium, they stock something that looks to be 1/4 inch plastic mesh in a few different sizes, you might call first to be sure they have one for you, they cut it into pieces and have them in bags and I am unsure if they have back stock if they are out of your size.
Get a piece bigger by many inches then you need.
This will be 10-15 dollars
Then go to home depot and purchase a screen building kit with the smaller screen size, there are two types of screen frames and they differ by the width of the channel you will be inserting the screen into and holding it in place with a rubber gasket, get the smaller size. Its obvious and stated on the package the two types are something like 3/16" and 5/16" or something like that. Also purchase the spline tool, I got the plastic one, its 3 dollars.
Cut your screen frame to 1.5 inches less than the exact OUTER dimensions of the aquarium glass (the instructions tell you this dimension, but I am almost CERTAIN its 1.5 inches less because each corner piece adds 3/4 " to the length of each side. Make two pieces for each dimension. SNAP in the end corners and you will have a square frame.
The metal frame comes in unfinished metal (silver aluminum), a nice brushed bronze and maybe black, so you can choose what you want.
Then lay the frame down on a carpet or some clean surface and starting in one corner lay your mesh over the frame with the slits that your going to push the mesh into facing up.
Since the mesh has nice straight lines, just push it about 1 inch over the edge of the frame along the long edge and get it more or less aligned then using the spline tool push it into the slits carefully pushing and pulling it so that you are following a line in the mesh along the long part of the frame. They instruct you to do this along the entire distance and then place the rubber gasket that holds it in place. This in my experience does not work well for the plastic since it pops out. So, once you have a few inches kinds bent/pushed into the frame, start with the black gasket and using the other end of the spline tool push it in over the top of the mesh and just use that to guide yourself down the length, when you get to the next corner be SURE to pull the mesh tight and follow the opposite grid on the mesh and continue around until you reach the ends. It will hold a little better if you cut the gasket when you get to the corners. When you done, you should have a taught mesh (some of the folds might be kinda evident for the packaging but they settle out) and then using a razor blade its SUPER easy to cut the extra mesh off the sides, just run the blade along the outside edge of the frame above the gasket. DO NOT SLIP AND CUT THE MESH IN THE FRAME!!! BAD MOJO>
I seriously doubt this will support a big cat if it wants to walk on water... but I guess you will post the results!
Total cost is probably < 25 bucks.