When you think about it, what God said he was going to do, and what He asked Noah to do was full on. Since the world was full of sin, maybe he would have only had help from the few people God intended to go into the ark. So it would have been a huge project on several levels. 
However it is written that Noah did exactly what God asked him to do. 

Apart from being part of the few God had chosen to spare, it could also been seen a privilege that God asked him to do something for him. God didn’t have to do it this way. He could have fixed it all himself. It is a privilege when we are asked to do something for Him. Not only can we be sure He doesn’t ask of us more than we can achieve, it shows He trusts is to do it.

What an honour and opportunity it is to serve the one who created everything. 

God knew what he was doing as he chose Noah to do the job. It was a “no room for error” project. And since God chose the right person, it all went as planned.

“Noah did everything just as God commanded him.”
– Genesis 6:22