Putting decking tiles on a concrete balcony roof

[EarSlaps]

We have a balcony on the front of our house. It is over the playroom (used to be the garage), had building control approval, structural engineer's drawings etc so we know it's ok to use.

It is pretty ugly at the moment (as was the rest of the house), so we would like to make more of a feature of it and were thinking of laying these and adding nicer chairs, a few plant pots etc. The tiles look fairly lightweight, so they shouldn't add too much extra load to the roof.

The roof is a concrete type surface, and a builder recommended some extra waterproofing on the top of it. A lot of the flat roof paints say they aren't suitable for foot traffic. However, if we are going to lay the decking tiles on top, then there won't actually be feet on the paint itself. The difference between waterproofing for flat roofs and waterproofing for foot traffic areas is ££££. We won't be using it lots and lots- a few evening drinks up there watching the sunset, the yearly firework displays etc.

Can we get away with just using a flat roof paint and then putting the tiles over the top? It would be more waterproofing than it has had for the last 12 years and we can't see any obvious signs of water damage. The tiles should be light and easy enough to take up to inspect the surface every now and then and shouldn't impede drainage.

I just don't want to do anything that could damage our house!