In one of my CS GO projects, I am planning on a theme that would make sense to have glass used throughout the map.
I really like the idea of making sections of the map give visibility without making either player vulnerable to bullets. This could be achieved through things like a room above a main section of the map with an unbreakable glass floor, having windows facing into mid/a bombsite with unbreakable glass etc. My main concern is wondering if players would find it frustrating to be able to see the enemy but not able to shoot them without further manoeuvering. Something like giving T's a way to see how many CTs are heading towards one of the sites, but without the long line of sight to be able shoot them. I like making CTs or Ts have to use smokes to prevent the other team getting information (like Dust 2 doors), but without it requiring an involved AWP battle.