Gyprock: Gyprock can have cracks along the joints over time and there can be sagging.
Plaster glass: Creases on the surface and sagging of the ceiling are the two most common issues with plaster glass.
Gyprock: Gyprock is very affordable.
Plaster glass: Plaster glass is very expensive to install, but worth every penny with the details and character it provides.
Pros and Cons
Gyprock: Gyprock is cheap and easy to install. However, many issues can arise if it is not installed properly. It also absorbs moisture, which can cause even more issues in the future.
Plaster glass: Plaster glass ceilings last much longer once they are installed. They also add detail, character, and acoustic benefits to a room. The downsides to this material are that it is expensive to install and dirt can be absorbed by the ceiling near the top, which can make it look dirty over time.