Because my house decoration caused the roof to fall off downstairs, does the property undertake maintenance? Is it not a quality problem of the building?

The maintenance responsibility of the property is mainly the public part of the building/residential area. If this problem is caused by normal construction, it should belong to the problem of construction quality. In this case, the property has the responsibility to coordinate maintenance with the original development unit; But if this situation is caused by abnormal construction, I'm afraid you have to bear the main maintenance responsibility yourself.