kitchen ceiling is 13.5 ' x 13.5 '; starting in the middle of the room, as we have medallions in the design & lites coming thru the middle of them over the island. have already up there, sub ceiling & 2 layers of drywall. want to put up 2 x 2' tin ceiling tiles; during the overlapping, what happens when 4 corners meet - do u not have 4 layers of tin @ that point? how do u get around that so it doesnt look thicker than the other places? also, with the ceiling as described above, is it necessary to STILL apply more sub-ceiling? i am using adhesive & brad nails to apply the tiles. help????