There are several different reasons your roof might be leaking. Some signs of a leak are blistering paint on eaves or ceilings, brown stains, mould in one area and the most obvious sign, water coming in.
Here’s what I’d look for first:
Broken roof tiles or pointing that might be loose or cracked.
Tiles that may have moved or lifted from heavy winds or even from a possum or other animal.
Rust holes on the metal roof sheets and valleys.
One cause that’s often overlooked is debris that gets trapped in the valleys or between tiles. This acts like a dam and pushes water into places it shouldn’t go.
When it comes getting on a roof, safety is most important and all safety precautions should be strictly followed.
Personally, I think it’s best left to the professionals.