Lexan is stronger than Plexiglass.  Also Lexan is easier to polish out scratches with blue magic.  Plexiglass is cheaper though.
I usually order my lexan from mcmaster carr book but I know lowes and home depot have an area.
But it is hard to find an employee at those stores that can cut it correctly.  You can get a scoring knife for lexan and plexi glass and cut it yourself.
You score it with a straight edge (i know i am spelling score wrong but to lazy to spell check) and then hold it along a straight edge and litterally bend/snap it over the straight edge.  It works best if you score it then flip it over and bend/snap it over the straight edge.
For rounded corners you are going to need a router.
Hope that helps
Brent
www.extendedplayarcade.com