Interviewer instructions
The roofing materials for a house enhances the durability of the house as it protects the house from natural elements.
Roofing material is considered to be the one that protects the household from effects of nature. In the case of a flat where the top most floor has a tile roof, households that live in the top most floor will have their roofing material as tiles while all other households in the lower floors will have concrete as their roofing materials.
To deal with security issues, some households may construct a concrete roof on any house, which is not a flat, but cap it with tiles. For such households, their preferred roofing material is tile. Therefore the roof material for that household is tiles. The concrete is not actually meant for a roofing material but is an anti burglary mechanism.