Abilities costin resources

ive tried and tried but just cant seem to make certain abilities cost resources. Please help.

I don't know the exact syntax but something like:

Event: Unit casts spell (Your spell)
Conditions:
Actions: Add -100 Gold for Player(Owner of Triggering unit)

E - A unit begins casting (spell)
C - Gold of (owner of (casting unit)) (superior or equal) to (100)
A - Set (gold) of (owner of (casting unit)) equal to ((gold) of (owner of (casting unit) (-100)))

2nd trigger

E - A unit begins casting (spell)
C - Gold of (owner of (casting unit)) (inferior) to (100)
A - Order (casting unit) to (stop)

This can also be done in 1 trigger by a if/then/else if you want