Wiktionary
n. The finishing of a building's roof, often accompanied by a special ceremony.
Wikipedia
In building construction, topping out (sometimes referred to as topping off) is a builders' rite traditionally held when the last beam (or its equivalent) is placed atop a structure during its construction.
Nowadays the ceremony is often parlayed into a media event for public relations purposes.
After topping out, numerous elements of construction remain, including interior finish and most mechanical, electrical, and plumbing systems.
Usage examples of "topping out".
Giordino paused and glanced at three armored personnel carriers that sat in a row, squat and low, topping out at less than 2 meters.
Just as I was topping out on the rise a man raised up, rifle in hand.
The best was topping out in the apartment one time and watching the wallpaper.
Juvie--seven Richards--five Negro, two white--porkers topping out 250.
He was still in the hollow and out of sight if they looked back, so he climbed slowly, topping out on a rise to see them far ahead, driving fast.
They were topping out at the canyon's edge, and a far-off shout told me I'd been seen.
The attacker rose higher, topping out over the slope, and he wondered why they were no longer using their jump gear.
We held to low ground, keeping off skylines, finding a saddle here and there where we could cross over ridges without topping out where we could be seen.