Need help with an easy Spell

Hi there!
I want to make an Spell. I guess its quite easy to make but i somehow dont get it ^^
So the Spell should be like this:
When activated you can choose a like 600 AoE (like for example Blizzard).
Where it is casted there should be a big image on the floor. The imgae should be an aura (for example the life steal aura). Im not sure if you can make it bigger,if not the image should be there multiple times.
Now everyone who enters this area should take 50/100/150 damage per Second for 10 seconds.
It shouldnt be a percentage like Lich's Ultimate and it shouldnt be channeling.

Create a dummy unit using the life steal aura model with immolation.

Thanks worked fine :D