When Innistrad was first being spoiled, one card that caught my eye was Rooftop Storm. Reading the card, I thought it would be fun to pair it with Haakon, Stromgald Scourge...
The main crux of the deck is to get out Rooftop Storm and Haakon, and cast Zombies Knights out of my graveyard for free (Rooftop Storm makes Zombies free, Haakon allows me to cast knights from my graveyard). This is made more powerful if I have some way to either sacrifice for benefit, or a way to sacrifice and have a benefit from casting the creature over and over.
Apart from the main combo cards, I ensured that I would have creatures that, by default, I can cast over and over for free (apart from Haakon), so got Stillmoon Cavalier and Stromgald Crusader - they're good in the deck because if I'm casting everything for free, I'll have spare mana left over. I wanted to add Phyrexian Crusader (a much favoured card of mine), but it didn't fit with the rest of the deck that much, so it was eventually removed. I added a couple of ways to search, and some quick mana cards (to get up to 6 for Rooftop Storm), as well as a few other Zombies that help out.
4 Tainted Isle
4 Drowned Catacomb
1 Darkslick Shores
1 Dreadsheep Reef
4 Haakon, Stromgald Scourge
4 Rooftop Storm
4 Forbidden Alchemy
1 Diabolic Tutor
1 Null Profusion - Just a fun card. Allows me to draw lots of cards by playing things for free (extra cards by casting from my graveyard...)
4 Dark Ritual
4 Overeager Apprentice - Fun mini-combo: discard Haakon to the ability, use the three mana to cast the just discarded Haakon
4 Stromgald Crusader
2 Stillmoon Cavalier
4 Corpse Connoisseur - For finding a creature if I need to
2 Carrion Feeder - Sacrifice outlet (can be found with connoisseur so I didn't put 4 in)
3 Ashes of the Fallen - With all the Zombies in the deck, it is fun to set it to Knight :-)
1 Noxious Ghoul - prepare the field to attack
I was able to play a casual game with this, and did get the combo going. Interestingly, as there are a number of half decent Zombie creatures, I had done quite a bit of damage by the time I got a Rooftop Storm out, but it was still fun to play and put together nonetheless :-)