There seem to have been two versions of the story, one with animals in sevens, the other with twos, which were put together to make the final version, without much editing. So in Genesis 7:2-3 it's seven pairs of 'clean' animals (ie kosher species they could eat), seven pairs of the birds, and a single pair of 'unclean' animals. Then in verses 8-9, it's two of everything.
In any case, your above ark will have to be 300 cubits long, 50 wide and 30 high. It needs a roof, finished to 'a cubit above (above what?), a door in its side, and lower, second and third decks. It has to be made of gopher wood. If you don't get it right, maybe God won't protect you when he opens the trapdoors of heaven and lets loose the fountainsof the great deep. And yes, they really did believe the sky was a solid sheet of something or other, with water piled above it, and trapdoors to let the rain through.
