How do I make a boss health bar?

I have a boss and after a period of shots (30) I want him to be destroyed? How do I do this? Collision?

Create an instance number (Health) variable in the boss with a value of 30.

When your bullets/objects on collision with subtract 1 from the boss's (Health) variable.

The write a condition

Boss>Compare value (Health) < 0 (Less than or equal to 0 > Destroy Boss