I don't have any answers, but I believe what you want to build is called a "pony wall." If you google that term you will probably find lots of info.
Edited to add: I know you didn't ask this, but if this is your first time building a shower, please be sure you fully research and understand how to waterproof it. An improperly built shower can cause a whole lotta water damage before you even realize you have a problem.
Last edited by Blondesense; 02-28-2011 at 12:30 PM.
We would like to install a half wall with glass on top of it for our shower. It would only be anchored to one wall and not the ceiling.
You would need to bolt this 1/2 wall to both the floor and the wall. You should bolt this to studs in the wall and joists in the floor. If the 1/2 wall isn't aligned with both of these, you should install blocking between the studs and/or the joists.
Screw plywood to the 2 faces to increase rigidity of the wall.
This should stabilize the wall enough to build the top you want.