Hugh,
The key is the galvanized steel used in metal building construction (galvanized to prevent rust). Galvanized steel with the difference in electrical conductivity between zinc and iron makes a primitive capacitor but more importantly exhibits dielectric properties. From Wikipedia (to make it a simple explanation): A dielectric material (dielectric for short) is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material as they do in a conductor, but only slightly shift from their average equilibrium positions causing dielectric polarization. Because of dielectric polarization, positive charges are displaced toward the field and negative charges shift in the opposite direction.
As a result it tends to retain a charge rather than allowing it to flow to ground. This can create a catastrophic electrostatic discharge.
The addition of a woven copper mesh to the interior surface of the steel building makes a decent rfi protected building or faraday cage. Many U.S. government buildings are constructed using this method, though they tend to hang it inside the sheetrock walls. To prevent snooping they will run a low voltage DC current through the copper mesh, which actually improves its performance as a faraday cage.
If the building is to be built as a faraday cage then layering copper mesh into the cement floor (with an exposed edge for grounding the copper mesh) should be specified at the time of construction. Without the exposed edge to earth ground the floor can build up a floating charge, which has been the bane of many a data center operator.
Finally, the building has to be properly grounded using a copper grounding rod buried deep enough that it is down into constantly moist soils.