Rooftop Storm
Enchantment
You may pay 
rather than pay the mana cost for Zombie creature spells you cast.
"Let those idiot priests tremble! A new era in unlife begins here and now. Oglor, raise the lightning vane!" —Stitcher Geralf
John Stanko
Innistrad (ISD)
• #71Rulings
You must still pay any mandatory additional costs, such as exiling a creature card from your graveyard for Makeshift Mauler.
(wotc • 2011-09-22)
The mana cost and mana value of the spell are unchanged. Rooftop Storm only changes what you pay.
(wotc • 2011-09-22)
Rulings
You must still pay any mandatory additional costs, such as exiling a creature card from your graveyard for Makeshift Mauler.
(wotc • 2011-09-22)
The mana cost and mana value of the spell are unchanged. Rooftop Storm only changes what you pay.
(wotc • 2011-09-22)