On Monday, 9 May 2016 05:49:31 UTC+1, wrote:
I'm planning an extension to my house, and want to make flat roof that will last a long time, is maintenance-free and tough enough for people to walk around on, and is fairly light in colour on the surface.

Can anyone recommend cost-effective materials? I'd something rigid rather than joists and plywood with a waterproof covering, which, in my experience tends to have limited durability.

Many thanks..

J

Concrete roof slab and paving stones set in pitch is the commercial solution.