Never built one, but I can give a few pointers based on what I do know.
First of all you really don't want to use a visible light laser, an inferred or near infrared one is probably better since you can get pretty bright without being visibly noticeable. Though I don't know how reflective glass is to such wavelengths.
Also, if you want to actually hear anything any real distance away you'll probably need some form of optics to concentrate and likely collimate the light into your receptor.
Anyways, like I said I never built one so I can't give you any nitty gritty so sorry about that. Oh and on a related note your post reminded me about something I saw a few years back, this same principle can potentially be used to recover sound from even videos. https://www.youtube.com/watch?v=FKXOucXB4a8