Attention to a water leak prevention always gets the highest priority in my house. I would rather stop a leak than pay for damage caused by one. The most common leaks originate at roof openings for vent stacks, chimneys, skylights, or other similar items protruding through the surface. Grab a ladder, someone to cheer you on and go fix that leak.
Before you step on the roof be sure you are not going to do additional damage. Clay tiles can be extremely fragile. Severely curled shingles will break if you step on them, risking greater damage. They should not be loose, damaged, blistered or missing. Any hesitation about safety or doing damage should be heeded despite my urging to get on the roof.
Check the flashing around your chimney, skylights and other pipes (usually vents) that protrude through the roof. Water should not get through cracks. If you cannot visualize where a leak might be originating, pour a little water on and watch.
Check the chimney cap and mortar. The cap (which keeps sparks in and critters out) should be in place and clear of soot. The mortar between the bricks should not be cracked or missing. A chimney sweep has the skills and tools to assess and repair any chimney concerns you might have.
Check the gutters and down-spouts to be sure that they are attached and clear of debris (I just found a small pine tree growing in my gutter!). Be sure downspouts direct water away from the foundation.
Vents, louvers and chimneys should be clear of nests or insects. When you are finished, I would recommend making notes in a small notebook or computer file in case you find similar issues in the future.
Side Note: Years ago I thought I knew how to use a ladder. I probably thought I knew everything. I had been up and down ladders hundreds of times, and the ladder had only moved once or twice. Then, a fireman from Cape Cod taught me how to safely use an extension ladder. Before you climb your ladder, watch the video on the link below to see if you are doing it correctly. Pay particular attention to Tips 1&5. (www.familyhandyman.com/DIY-Projects/Home-Safety/Ladder-Safety/tips-and-techniques-for-safe-extension-ladder-setup-and-use/View-All).