you should really check out www.r1150r.org
(i'd paste the link but it always comes up r1150.org no matter what page you're on)
like i said, they have a rockster forum and there's a thread called "with or without winshield" and many people posted pics of their screens including a couple of people who've made their own. one guy made one from an old helmet shield. there's tons of info there for the rockster.
also if you go to A&S cycles, they have a few shields for the rock as well.
BTW, which rock do you have?