Roofer messed up? (coping stone on parapet wall)

Long time reader but first time poster - go easy please

We had a roofer put up some coping stones on a parapet wall around 6 months ago on the extension. 3 weeks ago, one of them fell into Neighbour's garden and then this week the remainder fell into the neighbours garden, luckily no one was hurt.

We have had another builder over to fix and he has said two things:

1 - coping stone on parapet wall were put in properly and the previously builder did not use adhesive which he was suppose to use and just concrete - is that right as I thought it was just concrete but it does make me wonder why the coping stones fell off under windy/rainy weather) Sample picture: it's something like this but instead of glass it is Spanish tiled roof. You'll be able to see from the pictures below.





2 - The Spanish tiles (Not sure if they are actually Spanish??) have been put in incorrectly as all the nails are still poking out. The new roofer is saying that the previous guy did not use the correct nails and also did not overlay the tiles which he saw suppose to. Apparently water is now collecting under the tiles and it is just a matter of time before the whole thing goes to sh*t.

Here are a few pictures...Grateful for what you guys think as he wanted to charge £1700 to fix all this.

Our extension is on the right hand side in the picture below:

Lol has this new roofer got a clue?
They are fibre cement slates and the copper tail rivet at the bottom should be showing. It is there to reduce wind uplift.

Not too sure why the coping stones have came off, maybe a too weak mix. Hard to tell without a picture.

Thank you, makes sense.

What is the copper tail rivet? I have googled but cant figured out what that is?

Google copper disc rivet and it will come up then.

Thanks

Sorry 1 more - does the gap between the slate OK? Is the overlay too little?

It`s all fine - Have you got a circus on a park nearby ? cuz your "builder" is a Clown £1700 for sweet FA

Interesting.. Thanks


How much would say it should be realistically?

The best capping you could have on that parapet would be sheet lead . Even if those coping stones were fixed immovably , the joints would fail one day and water would get in . Have a google for The Lead sheet association I am sure the rest of the roof is fine . You might even find a competent leadworker in London , I think maybe the regular poster Palaceray is a london roofer .