Large Flat roof, no leak, just supporting it's own garden!

[Strevs]

Hi, moved into house about 6 months ago and have noticed in that time that large rear flat roof that covers part of kitchen, breakfast room and lounge extension has got more and more plant growth on it.
Some is obviously moss whilst the other type have never seen before (has lots of spider web type roots)
Obviously doesn't look to good from rear windows but am more concerned about extra weight/damage etc.
The roof itself is covered with small stones that i presume were once white but now grey and roof looks like it's had partial repairs around the edges.
Is this as simple as just getting some "plant killing" solution and applying liberally or is it an indication that other things are wrong (too many stones, roof sinking, pitch wrong)
All advice gratefully received and will be digested!

 

[JohnD]

if it is holding water then the roof is sagging

might be it was built with undersized timbers

might be someone has removed an intermediate wall that was supporting it.

might be the extension was badly built

it is going to need some rebuilding.

if you can pull down some of the ceiling underneath you may get an idea of what has happened

the more ponding you have the heavier it wil be so the more it will sag.

start asking around for a good local builder or (flat) roofer and get them to take a look.

 

[noseall]

i think you've posted the correct answer to the wrong roof problem JohnD.

 

[JohnD]

you may be right.

I added the first sentence in an edit when I reconsidered