Here’s a link to Rose’s Chocolate Pavorati cake: http://www.realbakingwithrose.com/2012/06/a_new_cake_for_fathers_day.html.
Her Chocolate Domingo cake, which I like better, is also out on the blog (search “Chocolate Domingo”)—I can’t attach it because it’s a .pdf.
No need to do any special decoration for a birthday cake. You can make one layer or two. If you make one layer, you can dust it with powdered sugar, or you can frost just the top, or frost it all over. If you make two (or more) layers, you can frost just the top of each layer and stack, or you can continue on and frost the sides as well.
You can then sprinkle it with nuts, crushed candy bars—anything that you thing the recipient might like.
I never do any fancy decorating, myself. It’s not a skill I have, yet I make birthday cakes all the time!