Can you talk to me about roof terrace tiles?

[Primafacie]

We are hoping to buy a house that has a flat roof suitable to use as a roof terrace. The survey says we need to install some promenade tiles. I would like to put some hardwood timber tiles or if not possible, just regular promenade tiles. Does anyone know whether we need to put a waterproof membrane or anything underneath, or is it just a matter of fitting tiles on top of the existing asphalt cover?

I will get quotes but I am worried roofers/builders will try and take me for a ride with all sorts of extras I don't actually need. Any guidance would be much appreciated.

Is there planning permission in place?

Roof terraces notorious for getting knocked back at planning stage, though if already used as such with existing balustrading and access may not need pp.

Really no idea about whether laying tiles would damage the integrity of the asphalt wrt waterproofing/runoff. Also you'd need to be absolutely certain that extra weight of the tiles would be capable of being borne by the existing joists.