How do I end a level at a certain height?

Hi everybody! I am in the process of making a stacking game whereby a level ends once the stacked objects have reached/surpassed a certain height. The objects are stacked using the 'drag & drop' feature. I'm experiencing two problems:

1) Making the system recognize that my stacked objects has reached a designated height

2) Doing the above without accidentally triggering 'level end' should a player drag the object pass the intended height (I hope that made sense )

Any help is greatly appreaciated.

I guess you could add a boolean instance variable Stacked and set it to true when stacked

If there isn't a line yet add a detection sprite at the right y-coordinate

object is overlapping detection

object is stacked

level end