There are many different grades of what you are calling plexiglass. The stuff from your local hardware store is complete crap and unsafe for something like this. There are some that can withstand a rock or a bird impact but from what I have read on other forums this is still unsafe also as they have a tendancy of complete explosion from the impact. As sunsetdart said your state will probably not allow it. I would do some serious research about it first. What is wrong with proper safety automotive glass by the way ?