What kind of tile roof do you have? Terracotta? Slate? Ceramic?
All types of roofs in all types of climates are prone to leaking for a variety of reasons. From poor installation to improper use of material (even if the install is proper.) It may be best to have a professional roofer inspect your roof. Maybe 2 or 3 pros. You'll learn a lot by having them there and by asking questions.
My best to ya and hope this helps.
PS: After this afternoon, I won't be back until Tuesday morning but others will be 'around' ...