I have a leak in my bedroom ceiling which only occurs during prolonged or heavy rain. There is a terrace above but this has been fixed so it could be from the patio windows or the roof above the terrace.

Have you tried tracking the source of the leak? You might have to remove the ceiling tile and track the leak back to its source. Let me know what you find. Good luck, Tom

Roof leaks are one of the hardest things to trace. If you can't get into an attic space above the suspected area, you will need to open up the ceiling. However, the leak may be coming from another place and just dropping there. I would go above and look for every possible spot with a crack or start recaulking everything.