The advantage to plexiglass over plywood would have to be a splinter and weight issue as well as the fact that no one would be able to see your pride and joy rig at a gig. ( bad rhyme intended )
I think alot of you guys are a little hesitant of designing your own plexi shields-they are not that tough to make.
For a 4x12 cab go to home depot and ask for 2 pieces of 1/4" plexi cut to 20"x36".
Google Tap plastic and buy an acrylic hinge and the glue.
Cut the hinge to size I used snips-pruning shears would probally work, remember 36" is the hieght.
Glue the hinge onto the plexi one side at a time.
Thats it. You're done and that shield will last for years.
I like to round the corners of the plexi so they're not so sharp.
Thats all there is to it.
If you're still not sure, just bring a sheet of plexi and a hinge to my house in the summer along with a 12 pack of beer, and I'll do it for you. I'll supply the burgers.
Have fun,
Jack
Rock On and Keep the Faith
Jack Loves Patty Loves Joe