I don't know what a topping out party is.

Topping out is when the final piece of steel is installed on a building (usually a skyscraper). It is tradition in that case to have a tree, a flag and a party for the ironworkers and crew.

Surely you don't have ironworkers doing your house... do you?
How tall is your house that your consider it being 'topped out'?

I think there;s a similar tradition with residential timberframe construction so it's not a stretch to extend that to anything residential, regardless of height.

When we lived in Germany (40+ years ago), I learned that Germans always had such a party when building a house. The framers would carry a small pine tree up to the rooftop and sit around up there drinking beer when the last of the roof trusses was laid. The town we lived in was experiencing a building boomlet due to all the Americans who were being transferred there from France so it wasn't at all unusual to see what looked like Christmas trees tied to the rafters of a house under construction.

Hadn't thought about that tradition in 40 years. Thanks for the jog to the memory.

No iron workers at our house. Someone was telling me about it and I didn't know if it was something the framers would be expecting, bad karma not to do, or a nice gesture. It's a 1-1/2 store home.

Alcohol on a construction site is not a good idea for a number of reasons. Have the party when the house is finished.