From the Days of Noah: Before the Flood

Whenever I read chapters 5 to 7 in the book Genesis in the Bible, I was confused that God judged human beings by the flood. My eyes always stopped at the verse 5 of chapter 6, "The intention of man's heart was evil from childhood; they thought evil at all times, imaging evil from morning to night. (My version)" Is that the main reason?
I have tried to find out what evil they always thought and imagined: violence, raping, murdering, lying, deceiving, or something terrible.
This novel is like a journey to find out the most wicked thing to the eyes of the Lord. When I wrote more stories, I realized that people grew more wicked than before as cities were bigger and civilization flourished more. Finally, I found out one important thing that the Lord could not help but punish the entire earth by flooding even though he really loved the world so much. Fortunately, Noah was different, found favor in the eyes of the Lord, who is our ancestor.
Jesus says, "As it was in the days of Noah, so it will be at the coming of the Son of Man. (Mat-thew 24:37, NIV)" I have wondered how people in the days of Noah lived. Inspired, when I pictured what the most wicked thing was, how it started to rain for the first time, how a gopher-wood ship was coated with pitch, and what fruit the Tree-of-Life looked like, I decided to write this novel. It starts with a story of the day when Noah was born and then three innocent brothers were tragically murdered at the Maadan of Light.