Building a strong record of the damage
You prove structural damage with documentation: dated photos and videos showing the damage and how it changes over time, written reports to your landlord, any inspection or code-enforcement records, and medical records or receipts if it caused injury or loss.
Structural problems often worsen, so photos over time are powerful — showing a crack growing or a balcony deteriorating. Save every text and email with your landlord, since these show what the landlord knew and when.
If a building inspector was involved, keep their reports, which can carry real weight because they come from an official source. Note the dates and describe the danger clearly. If anyone was hurt, keep medical records and photos of the scene and the defect. A free review can help you understand which evidence matters most in your situation.
This is general information about California tenant rights, not legal advice. Every situation is different.