West facing windows present much greater dangers when it comes to overheating as by the time the sun shines in them the property is already hot. When the sun does shine in it is at a low angle and can efficiently overheat internal parts of the building.

Too much glass is another problem, the best mitigation is to externally shade the glazing.

Regarding rooms in the roof, these are rarely well enough insulated to prevent overheating though they can be.

I don’t see ridge ventilation as the answer, it could help a bit but the problems are not easy to solve and the basic idea of a room in the roof is not fail safe or even a good idea in my way of thinking. (Often too cold in winter too)

I wouldn't write off room-in-roof for either summer overheating or winter heat-loss reasons. We know perfectly well how to new-build or thorough-refurb to prevent both those problems, and as a space-enclosing method is supremely easy and economical, as well as (if you want 'in principle') minimising useful-floor-space-to-external-heat-loss-area ratio.

But their E-S-W sun-facing tiled/slated slope(s) does get super-hot; we then rely on copious through-ventilation of the tile/slate batten space to cool it. As a convective chimney-effect space, that is very efficient, if done right. My habit is to run 35x50s as downslope battens, above the underslating/breather felt, beneath the 25x50 slating battens (which I consider equiv to a 50mm void overall) - a vent zone completely uninterrupted from eave to ridge to opposite eave, including planned generous ventilation routes around Veluxes, hips and other interruptions. Continuous 25mm-equiv vent inlet Glidevale FV250 or equiv at both eaves; and same at valley/gutter board edges and at the ridge tiles (unfortunately not so easy). So yes, 25mm ridge ventilation (not just the 10mm reqd by Bldg Regs) is essential (but a waste of time unless the zone continuity is perfect).

Then, as well as plenty of insulation beneath the breather felt, the other neglected essential is airtightness. The other day, viewing a 25yo room-in-roof barn conversion, stinking hot, the jets of superheated air convecting through hairline cracks along the exposed purlins/plasterboard joint could be felt, and visible as accumulations of dust along the line. The power of convection at the very high temp differential between too-hot-to-touch unventilated slates, and the relatively cool interior, should not be underestimated. What to prescribe? With slating still in good condition, stuck with old fashioned non-breather underslating felt, only with a considerably lowered sloping ceiling could a proper cure be provided.