Building below ground?
I came across these links the other day, and it struck me that shifting a proportion of residents and even some commercial activity underground might well be defencible on a number of grounds (no pun intended).
From a residential point of view, you're certainly going to pay more in form work and excavation.
On the other hand, you can choose structural materials according to their strength, impermeability to water, and low cost rather than their external appearance. You could, in theory, have a house, the outer walls of which were made of Besser block, broken brick and form work from building sites and PVC. You'd never need to paint, or fix a roof or gutter, and the house would be secure from fire, storms, and perhaps even more secure from burglary. You might never have to pay to heat or cool the place, and pay a lot less for hot water. You could have heat pumps supply you with hot water or cooling as needed.
I see light and air being brought in through large mushroom-shaped skylights made of perspex above each room, with the domes being six feet (1.8m across) with reflective sides and flywire on the under sides to permit airflow.
You could even grow stuff on parts of your roof. Grow some pleasant smelling plants near the domes, and the house is scented.
On a larger scale, you could build eco-housing states and even shopping complexes the same way.