Did you try to use the ventilation fan? Also, how about your roof? Are you using tiles or metal roof?

My goodness, I am going to have metal roof too.

My contractor is suggesting one single layer of aluminium insulation. I asked for more and he recommended Sun-foil reflective aluminium bonded with a layer of 25mm FR polyethylene bubble sheet and woven fabric. I am considerng three other options:

(1) the solar-powered turbines. But, have not decided yet.
(2) the solar panel to generates electricity, which can act as an extra layer.
(3) heat reflective paint. But, it may have an issue for the warranty of the metal roof.

Oh, a bit too late from me.

My renovation has been approved and my contractor has started. Mine is a semi D facing north west. Afternoon sun is a concern.

Thanks for the idea. Ya, I am thinking of light grey metal roof. For the master bedroom, I am thinking of the external heat resistance paint and also plan to plant some trees.