How to Tile Irregular Sized Rooms

Locate the farthest, full wall from the door of the room to be tiled. Measure the wall and find the wall's mid-point. Mark the mid-point with a pencil, on the wall above the floor.

Lay the tiles to be installed straight along the maked wall in a dry layout, meaning without mortar and before any cuts have been made. Lay the first tile so its center lines up with the center of the marked wall.

Lay the tiles in the dry layout evenly out from the center tile to each side of the room, and mark each tile that will need to be cut to fit on either end with the straight edge and pencil.
Continue laying the tiles in a dry layout backwards into the room, towards the door, continuing to lay from the center out to the sides of the room, and marking each tile that will need to be cut. Follow the room's angles outward toward the door by keeping the tiles even from the starting point; it won't matter if one side gets fewer tiles than the other, or if the room gets larger across as it moves toward the door, provided the beginning of the installation is even.

Cut the tiles that have been marked on the wet saw and return them to the dry layout. Inspect the dry layout to ensure that the tiles will fit, and that enough room has been left between each tile for a grout joint. Adjust the tiles as needed.

Lay the tiles in the same order determined by the dry layout by spreading a small amount of thin set on the floor with the trowel, once again moving from the center of the back wall out toward the door.

Allow the thin set to cure for 24 hours, then grout the tiles by packing the grout into the joints with a grout float.