We don't really know what the interior of the Ark looked like, because there is no detailed description in the Bible of the interior of the Ark. This is what it could have looked like. When Rod built his model he had to work out what it could have looked like, based on the needs of providing space for animals. The entire model is built to scale.

In this picture you can see a ramp leading from one deck to a lower deck and then another ramp leading to an even lower deck. You can also see some of the animal stalls.