Genesis 6:14 (ESV) Make yourself an ark of gopher wood. Make rooms in the ark, and cover it inside and out with pitch. 15 This is how you are to make it: the length of the ark 300 cubits, its breadth 50 cubits, and its height 30 cubits. 16 Make a roof for the ark, and finish it to a cubit above, and set the door of the ark in its side. Make it with lower, second, and third decks.
The above is the specs for the ark. It was 450 ft long, 75 ft wide, and 45 ft high. It was made of gopher wood. Gopher wood appears once in the scriptures and is not defined in the Hebrew. It is widely accepted to be either cedar or cypress.
It was covered (inside and out) with pitch. (Pitch, in Hebrew is an interesting word study that I will leave to you). It had three decks with approximately 15 ft between each. It was also covered by a roof that was approximately 18 in above the sides. There has been a lot of discussion about the 18 in space between the roof and the side. It also had only one door.
Noah, had the architect of the universe to guide his construction, gather the animals, and seal the ark for a year.
If you go to visit the Ark Encounter, and I recommend that you do, please keep in mind that this replica in no way resembles the actual ark. Imagine what the inside would look like with all the animals of the world in it at the same time. Only God could put them on the ark and keep them from tearing it apart, or killing each other.