You can use any seasoned natural hard wood like teak , sal wood etc. Another alternative is acacia wood (cost effective)!

Pradeep, plywood or Gypsum has little do with heat reduction . It is the air layer between the actual ceiling and the false ceiling that does bring the temperature down. So as long as you are having a gap of 4-6 inches between the two ceilings it shouldn't matter. Gypsum would be more cost effective. Thanks, Nitin CORNERSTONE DESIGNS, Bangalore

Nadia, You need to provide some more snaps showing the entire room, including the location of the beam, its height & clear height of the slab etc. One idea could be to extend the width of the beam by just about 25 mm with gypsum board on either sides, at the bottom level, with a right angular vertical of 25 mm as well & provide LED lighting strip for indirect lighting...

Suraj, If you have access to the room that you shared earlier you can try seeing the flicker effect at night time with both lights and fan being on. If the lamp has a 360 degree light spread it will cast the fans shadow on the ceiling and when the fan is turned on it causes a flikr effect. I personally find it a distraction and at the same time many would not even notice it. Take the pick based on your usage. Wall mounted fans and recessed fans can also be explored. Thanks, Nitin Cornerstone Designs, Bangalore.