Final answer:
The squatters do not have to pay anything to 'own' the building.
Step-by-step explanation:
In the text provided, it is mentioned that the building Rose Mary calls home is owned by someone else. The person questioning Rose Mary asks if she pays rent or taxes for the property, implying that she does not have the right to live there without contributing. Therefore, it can be inferred that the squatters living in the building do not own it and do not have to pay anything to 'own' it.