Here is a 0 rare starter framework for a Zoo deck.
2x Soulfire
2x Abusive Sergeant
2x Argent Squire
2x Flame Imp
2x Voidwalker
2x Dire Wolf Alpha
2x Haunted Creeper
2x Nerubian Egg
2x Harvest Golem
2x Shattered Sun Cleric
2x Dark Iron Dwarf
Those are all commons except Nerubian Egg, which is a free 'rare' you get with the first wing of Naxxramas.
The following rares would be your highest priority to finish the deck
2x Knife Juggler - These are ubiquitous and can go in many decks
2x Doomguard - These will only ever be played in Zoo, but they are incredibly powerful and a big part of the deck's ability to put games away.
2x Defender of Argus - These are ubiquitous and can go in many decks
As an alternative to Doomguard
2x Argent Commander - These can be played a bit more widely than Doomguard, so if you're new and leery about spending 200 dust on something that will only be played in a single deck, you can craft these instead.
So your finished list would look something like this
2x Soulfire
2x Abusive Sergeant
2x Argent Squire
2x Flame Imp
2x Voidwalker
2x Dire Wolf Alpha
2x Haunted Creeper
2x Knife Juggler
2x Nerubian Egg
2x Harvest Golem
2x Shattered Sun Cleric
2x Dark Iron Dwarf
2x Defender of Argus
2x Doomguard
1x Loatheb
With one open utility spot. You could stick in Power Overwhelming for more burst and another way to pop Nerubian Eggs, Mortal Coil or Elven Archer for removal, or Amani Berserker/Faerie Dragon for extra muscle. If you don't have Loatheb (From second quarter of Naxx) treat it as two open utility spots.