They probably they are. They have to show they have done everything a reasonable building owner would do to prevent such damage.
But if the roof was checked recently and was sound, or if the tiles came off due to a storm, they might not be legally liable and so their liability insurance won’t pay the claim. If the tiles were left loose by a cowboy roofer a couple of days ago, the roofer is potentially liable, not the occupier.
They might be/feel morally liable, but you can’t get moral liability insurance.
I was just clumsily pointing out that it’s a legal matter, not contractual, and might not be as straight forward as you would like.