Invisiability Area effect?

i want a spell that gives invisibilty an area affect and you can place it like a blizzard, i based the spell off blizzard but it doesn't work, and i changed the action to invisiabilty, does anyone think this is possibble? any special things i need to change?

with triggers maybe. you could say units under effect, blah blah blah, give invisiblity

oh cool, i'll check that out thanks :)