I am not going to say much about the first couple of verses. I wrote previously about the Nephilim and the giants of the Old Testament. Many people think that angels came down and had children with humans, which resulted in the Nephilim. However the wording of verse 4 makes it seem that they were already around. Of course we can only guess about the identity of the sons of God.
What I am amazed at in Genesis 6 is that men had strayed so far from the will of God that God wanted to kill all of them except one. Hopefully we never get that far again. Of course assuming God is sovereign, He knew that this was coming.
I wonder if Noah had any prior experience building a boat. If God told me right now to build a boat, especially one that big, I would run into some difficulties. It shows an enormous amount of faith I think, because it probably took a lot of time away from other things such as providing for his family and Noah is the only one God told. Noah also doesn’t show the concern with details that Moses would show later when God commanded him. Noah just does it and assumes it will work out since he was doing God’s will.