Not exactly a DIY question (yet, at least), but I am sure the combined
knowledge here will produce the answers that I am after...

I in the process of putting down an offer for a house in the (always wet)
west of Scotland.

The house is quite "different" from your average detached house in the area,
as it is the result of some design competition from the 1930's, and is of
Art Deco style. The house looks very sound in general.

The only concern I have is that the roof of the entire house (4 bed) if
flat. The owners assured me that the roof has been done up completely
earlier this year, and the work carries a 10-year guarantee. So far, so good
(my solicitor will put that as a condition to the offer).

However, during viewing I was looking down from the second floor window at
the roof of the single-story extension at the back (also new roof), in a
very rainy day may I add, showed that the whole extension roof was basically
one big shallow paddle (at least 0.5 " deep I would estimate). I haven't had
a chance to look at the roof of the rest of the building. Is this
common/what one should expect with a flat roof? or is it just a matter of
time before it will start leaking?

Also, what should I look for in a flat roof to put my mind at rest?

Whilst having a guarantee is reassuring, the thought of having to decorate
after each leak appears is not particularly appealing...

Any thoughts/comments will be much appreciated.

TIA,

J.