Here are some options.
This would be a traditional cowl, without any black makeup around the eyes (think Adam West):
This one is pretty much how it's been done in live action since B89:
This would be the same as above, but with all white contacts. I'm not a fan. A person's natural eye shape just doesn't look right when trying to allude to the comic book look:
Stylized lenses, simple, flat white:
Stylized with a glass like finish:
Stylized, if for some reason someone might want the eyes to glow:
I think retractable lenses could work well for scenes where Batman might need to use night or infrared vision. Personally, I'd love to see one shot where all you see is a black silhouette and the gleam of the eyes. I wouldn't want permanent lenses, though.