Rooftop Storm

Oracle Text

You may pay 0 rather than pay the mana cost for Zombie creature spells you cast.

Card Rulings

9/22/2011 You must still pay any mandatory additional costs, such as exiling a creature card from your graveyard for Makeshift Mauler.
9/22/2011 The mana cost and converted mana cost of the spell are unchanged. Rooftop Storm only changes what you pay.