You can do it couple of different ways. 1. Just cut and install the last tile and caulk the seam. (This option is not ideal and would not be recommended) 2. We offer a Plain Filler Tile that you can use as a border around the perimeter of the room so that you don't need to cut into the design(the tile can be used on its own). Either way you decide to go, using the filler tile or not, to completely finish the ceiling, you need to use crown molding. We offer beautiful Styrofoam Crown Molding..