I used 1/4" plywood for my 1955 Sportsman windshield pattern. With a crisp cut edge, it makes the glass guy's work easier. Don't forget to have the top edge radiused and polished as it is exposed and you don't want a sharp edge there. Also use auto safety glass if possible.
1966 Lyman Cruisette 25 foot "Serenity Now!"
1953 Chris Craft Sportsman 22 foot "Summerwind"