I have purchased a little stone house in Mallorca and need to insulate the roof as it is like an oven in the summertime and very cold in winter. The walls are 600mm thick stone so no issues with those! The roof has been renovated with concrete beams (horrible!), terracotta rectangular flat tiles on top of the beams and then typical red arab tiles overlapped on top to form the outer roof. I am thinking of using polystyrene panels covered in aluminium foil to reflect the heat and then building a wooden framework over the beams internally to attach thermal plasterboards to. Would this provide a really good level of insulation?