I ended up making two versions--both of which did indeed fly, although with varying levels of success.
The smaller of the two versions is 4 feet in diameter and weights 3 pounds, 7 ounces. This version has proven to be extremely durable and it flies perfectly. Plus it was relatively easy to make, as well as to throw.
The second version is 8 feet in diameter, and weighs a whopping 15 pounds. This beast will actually fly, but it is terribly tricky to throw. To get any substantial flight distance out of it, it has to be launched from either the top of a cliff, or from a long, steep hill. It's not the most practical thing, but I had fun making it and figuring out how to fly it.
I highly recommend making the 4-foot version, and have included full instructions on how to make one. I have included some basic information on how the 8-foot version was made as well, if anyone is so inclined to make their own super-jumbo frisbee.
Here are videos of both versions of my homemade giant flying discs in action.