Building coverage is the part of a flood insurance policy that pays for flood damage to the physical structure of a home: the foundation, walls, electrical and plumbing systems, furnace, water heater, and built-in appliances and cabinetry. It is separate from contents coverage, which covers your belongings.
Under the National Flood Insurance Program, building and contents coverage are bought as two distinct limits, and a policy can include one or both.
Example: a river overflows and floods a first floor, ruining the furnace and drywall. Building coverage pays to replace the structural elements; the homeowner's damaged furniture is a separate contents claim.
Related: contents coverage, NFIP, flood zone. See the flood insurance overview.