Actually the Bible does detail the size of the Ark in Genesis 6:15. 300 Cubits long, 50 cubits wide and 30 cubits tall. Basically, 450 feet long, 75 feet wide and 45 feet tall. It was a very large ship. Furthermore it could've been larger because there were larger measurements for a cubit than used today.
Also, there is enough water to flood the Earth in a current frozen state at both poles and spring water. Both under land and under the ocean.
It's unknown really how long it took Noah to build the ark with the help of his sons and others. Some believe 120 years but that's really how long before the flood that God gave the prophecy. A lot of scholars believe it took 2-3 years. A Dutch man built an ark 150 cubits long, half the size, mostly by himself and it took him less than 2 years. There are pictures of it, it's massive and holds a theater inside.
Noah was on the ark for 375 days, 370 days if using the Hebrew calender.