How to detect if a unit has hit/touched a wall/tree/building

[LearningCode]

I was thinking of making a spell that creates a giant ball xD
The 'summoned' ball cannot be controlled.

The giant ball rolls over enemy units and damages them.
The ball bounces off walls, trees and buildings (Doodads, structures and cliffs basically)
The ball continues that until its "Life-time" expires

But I have no idea how I would go about detecting if a unit has touched or hit a doodad/cliff/structure =/

 

[GetTriggerUnit-]

For trees, it would be something like Grouping Destructable around the ball, if there are some, make the ball bounce.

For unit, it would be something like Grouping Unit around the ball, if there are some, check if the unit-type is structure and finally, make it bounce.

For cliffs, maybe put invisible flying units where there are cliffs, make it bounce, etc..

 

[LearningCode]

It be good plan.
Gonna' work on that little spell once I am finished with my bag of chips.

 

[GetTriggerUnit-]

It be good plan.
Gonna' work on that little spell once I am finished with my bag of chips.

Of course.