Homeowner associations can compel homeowners to pay a share of common expenses, usually per-unit or based on square footage. These expenses generally arise from common property, which varies dramatically depending on the type of association. Some associations are, quite literally, towns, complete with private roads, services, utilities, amenities, community buildings, pools, and even schools. Many condominium associations consider the roofs and exteriors of the structures as the responsibility of the association. Other associations have no common property, but may charge for services or other matters.