Read Genesis 6-9
The story of Noah and the Ark appears to be an entertaining story for children. However, this is a story about evil spirit beings involved with human beings, thus causing the humans to live out their basic evil nature. God began to see the extent of human wickedness and that man's trend and direction men's life was toward evil, God regretted having made man in the first place. God's holiness could not contend with man's ungodly behavior and began to call it quits with man.
We get a first glimpse of an angry, but awesome God. God's first reaction was to cut man's life span from several hundred years of life down to only one hundred and twenty years. This reduction in man's life continues, the more man sins, the shorter is his life's span becomes (Gen 6:3).
Not only did sexual sins become a big issue with God, but also the evil giants being born (v.4). Goliath and his giant brothers were examples of such evil men (Num 13:33). Here we have former heavenly being (angels) mixing with earthly human being, which is a disgrace and forbidden by God. God, now regretting having made man, is now set to destroy him from the face of the earth. God has now conceived a plan to do this and He plans to do this by sending great flood waters upon the surface of the earth for the world had become rotten to the core (Gen 6:7; 11-13).
One may ask, why would God create a man who would sin to the point, thus causing the Creator, God to destroy the beautiful world He had just created more than 1650 years earlier? God could not have created man no other way except one capable of making moral choices. We see the results of what happens when man makes bad moral choices. Not only did God see what could happen if man made bad morale choices, God also saw what could happen if man made good choices. God's gift of freewill to man allows man to make the moral call. Else, we be nothing but fleshly robots. Being a robot is not a part of God's spiritual, and creative character.
God gave Noah instruction as to how to build the 450 feet long, by 75 feet wide, 45 feet high ark. Given the day and the times it was estimated more than 7000 species of animals along with food could be put upon such a boat (Gen 6:14-16). God promised Noah safe passage along with his wife and family (Gen 6:8-10,18). This is the very same promise given to each of us today by our Lord when we choose to accept Him into our personal lives. Noah constructed the ark for more than 120 years when there was no sign of a flood. You can imagine men scoffed him while he constructed the boat in the middle of the desert. The people had never experienced rain and did not realize that in God's time and in spite of being warned it was going to rain on their sinful parade.