Measure the length and width of the ceiling. If the room has an alcove leading into it, measure that section of the ceiling separately.
Cut the rug into 12-inch squares. Apply carpet glue to cut edges of the rug squares and let them dry.
Mark the center of one edge of the ceiling with chalk. Place the center of one tile against the mark at the edge of the ceiling. Make a mark at each edge of the tile. Draw lines from the marks on each side of the tile to the opposite edge of the wall.
Repeat Step 3 for the remaining edges. The lines create a crosshair at the center of the ceiling.
Place a rug square at the center of the cross hair. Staple along the edges of the tile. Place the staples about 3 inches apart.
Place the next tile against one edge of the first tile and staple it to the ceiling. Continue installing the remaining tiles from this center tile until you reach the edges of the ceiling.
Measure the space left at the edges of the ceiling if it is smaller than the height of the tiles. Cut the remaining carpet tiles to fit the space. Staple them to the ceiling.