The ceiling is tiled. In addition, it is framed out of level so that water will run down ceiling towards wall. This is common practice when the shower has a steam unit and is required per manufacturers specifications. We only use cement board or lath and mud bed in all of our shower installations to insure that the substrate is impervious to damage from any water intrusion. Another good system is the "Schluter" products. Hope this helps and good luck with your project.