In a setting I'm working on, a raised megacity the size of Switzerland (roughly 300,000 square kilometres) serves as the last refuge of humanity on a planet entirely covered by a global ocean. An unbroken ring of reinforced seawalls protects some eight million humans from skyscraper-tall waves, country-sized hurricanes, and the mind-warping effects of the ocean itself.
Despite this barricade, the inhabitants find their sanctuary frequently bombarded by storms of varying severity, to the point where gale-force winds and torrential rain are just accepted as a part of everyday life. How would the architecture of the city change to accommodate these environmental hazards?
Keep in mind that technology on the Wheel is very limited. The structure itself is held by its inhabitants to be the product of divine intervention, so that can be handwaved for now. Though their scientific advancement was in theory frozen at roughly the equivalent of Europe in 1920, the scarcity of resources means that in practice, most civilians only make regular use of technology that would be available a century before. Metal is valuable to the point where a steel sewing needle or a wrought-iron kettle would be considered a cherished heirloom. Machined objects are only made at the very heart of the city, in the heavily-fortified industrial core.
What would be the most cost-efficient materials and architectural techniques for the city to adopt, given these environmental and technical limitations?