The ark could easily have been built. I am not certain that this is exclusively what is being debated. The understanding of astronomy, calendars, weight, leverage, geology, and science in general was understood at an extraordinary level. Our modern structures require yearly maintenance at a minimum. The pyramids have stood for thousands with none, withstanding earthquakes that have leveled Cairo. The how is the mystery. The fact that they could be and were constructed is not.
Are there any findings of tools that indicate lesser intelligence in our species? Even the oldowan stones found near Lake Turkana is beyond what any primate has devised. I don't want to derail this into an evolution vs creation thread. Please ignore this and continue with the discussion—I am following with high interest.
It's easy once you know how to do it. Less mastery of a technology doesn't mean less intelligence. One feature of more primitive culture is that they lack specialization. They may not have specialized biochemists, but their man often master a greater number of skills from agriculture to manufacturing and construction. That means that a small team of their men would be able to construct their houses from commodity to finished building. Today you just have a larger number of specialists involved, which increases overall productivity with people knowing more about less and are able to repeat more work within given time, but it also means they may just know less in total.