ceiling,,that is "V" groove bead board. Accomplished by purchasing standard bead board and merely flipping the board over and installing it with the bead up - which leaves just the "V" joint visible between each strip. Just need to be sure to find product that has a reasonably clean back side - as that becomes your finished surface. Don't want to have to sand all of those if you can help it!. Then just lay trim over to create the impression of "coffers"