#a roof for the ark

This was probably a peaked or slanted roof. Its purpose was to protect everything in the ark from the rain.

#cubit

See how you translated this in [[:en:bible:notes:gen:06:13|6:15]].

#a lower, a second, and a third deck

"a lower deck, a middle deck, and an upper deck" or "three decks inside" (UDB) or "three levels"

#deck

"floor" or "story" or "level" or "room"

#Listen

God said this in order to emphasize that he would do what he was about to say. "Pay attention" or "Listen to what I am saying."

#all flesh

Translate these words as in [[:en:bible:notes:gen:06:11|6:12]].

#that has in it the breath of life

The word "breath" is a metonym for life: "that lives." (See: [[:en:ta:vol2:translate:figs_metonymy]])