1) only the bedroom are installed with air conditioner, and one side of the wall is east facing, which can trap heat throughout the day.
2) yes, there is a false ceiling below the roof itself. when i checked the roof through the service duct, i realised that there was some aluminium sheet installed under the roof tiles.
3) the space is roughly 2m from the apex of the roof, decreasing towards the edges of the roof.
i got the 2 inch duroone 0.6 x 4m insulation wool from homeone and man, it did make significant difference to the temperature within the living area in the house.
however the east facing wall still trapped heat, so my next home improvement project is the insulate the wall.