“Make a ship.” We do not know how long it took Noah to build the ark. It is often taught that it took Noah 120 years, but that is not correct. Noah’s sons were grown and married when God told him to build the ark, and Shem, Noah’s middle son, was 100 years old two years after the flood. So if we assume that Shem was around 20 years old when God told Noah to build the ark and get on board with his family, including his sons’ wives, then Noah would have been building the ark for less than 80 years, but it could have been considerably less than 80 years, the Bible does not say how long it took.
[For more on the chronology of Noah and his sons, see commentary on Gen. 5:32; 10:21; and 11:10]
“gopher wood.” The identity of gopher wood is unknown, although guesses and suppositions about exactly what kind of wood it is have been made. Since we do not know all the kinds of trees that existed before the Flood, and do not have Noah’s ark from which we could examine a sample, it is best to just leave the text “gopher wood.”