You can also use clear thermaform type plastic sheets to copy kit windshields and windows.
http://www.squadron.com/ItemDetails.asp?item=SQ9003
Take the windshield to be copied, and mount it pedistle style face up on your workbench. A big chunk of modeling clay and a large sized bottle of Tamiya acrylic works fine for this. Gently heat a piece of thermaform at least several inches longer and wider than the windshield, until it's nice and flexible. Then, place it over the windshield, and pull it's edges down past the windshield. It cools pretty rapidly, and will hold the shape it cools in. This is called 'smash' molding, and works essentially like a poor man's vacuum-former. Trim it to shape, and install.