In this sentence, "Over the years, they’d built snow forts together and leaped off backyard sheds together" what does "leap off" mean?
Without knowing the context more fully, this is a bit of a guess, but here goes:
The fact that the phrase describes the people building snow forts together leads me to think the entire description is during winter. Given the right conditions, snow can form a soft surface to jump onto.
The sentence definitely means the people jumped off the shed roof onto the ground together, but may imply that it was done into a snow pack for cushioning or lessened distance to fall. This is an activity children, in testing their daring, engage in. The passage therefore describes bonding through exciting activity.