Windows are fairly easy to incorporate into a tile situation. We have travertine in one bath and marble in another. The tile is set on durock backer-board with thinset that is attached to the drywall. The extra thickness is easily trimmed with tile. The windows are completely framed in (boxed in) with the tile and the grout is sealed. This allows the window to be in the shower area and protects the walls. If water runs to the windows it either drains to the shower or goes through the window weep-holes. The tiled window makes a pretty handy ledge for storing shampoo, soap etc.