Just finished making this thing. Used an old thick plastic cutting board, and traced my chainring on it and cut it out. Drilled a couple holes and it was finished. I had to use double space chainring bolts since its sitting on the front ring of the spider. I haven't got a chance to test it out yet, but we'll see how long it takes till it cracks in half.
Its not the most round or true bash guard ever, but hopefully it will get the job done.