"And God said unto Noah… Make thee an ark… Thus did Noah; according to all that God commanded him, so he did."
GENESIS 6:13, 14, 22
The Bible doesn’t tell us that Noah and his sons built the Ark all by themselves; Noah could have hired skilled laborers. There is, however, no reason to believe they could not, or did not, build the Ark in just a few years.
The strength and mental prowess of men in Noah’s day, was at least as great as, and quite likely even superior to, our own. They certainly would have had efficient means for harvesting and cutting timber, as well as for shaping, transporting and erecting the massive beams and boards required.
One or two men today can erect a large house in just 12 weeks, how much more could three or four men do in a few years? Adam’s descendents were making complex musical instruments, forging metal, and building cities. Their tools, machines, and techniques were not inferior to the ones we use today.
It is evident from examining the “mysteries” of earlier civilizations that the human race has likely lost just as much (maybe even more) knowledge from before the Flood, as we have gained since that time. The idea that ancient generations were more primitive than ours is an evolutionary concept.
When God first created Adam, he was perfect. Today, human intellect has suffered from 6,000 years of sin and decay, though computers are compensating a great deal for our natural decline in mental prowess, allowing us to gather and store information as, perhaps, never before.