Here is a Noah's Ark cake I made for one of my boys. The picture wasn't very clear and I kind of messed it up when I put blue icing on the roof and sides. But it was past 7pm and we hadn't had dinner yet.
This cake was inspired by Family Fun's Pirate Ship Cake, which uses a round cake pan, not a fancy one you will never use again. For this cake, I made a sweet potato cake with maple icing. The blue icing was made from white store-bought icing. I roughly mixed the blue coloring in so that it would give variations to the ocean color and the white sea foam. I spread it with a spatula and then piped around the base of the cake with a star tip. I can't remember if I piped some swirls in the ocean.
Oh, and I used Wilton's Noah's Ark mini cookie cutter set for the animals. Of course, regular animal crackers would do.
Below are the instructions (with variations). This doesn't have to be a birthday cake either. I've seen Noah's Ark as baby shower themes and I'm sure you could find more applications. If you try this, please let me know. I'd like to know how it came out (even if it was a nightmare).
(click on image for a larger -- and hopefully printable -- view)