I attended the "topping out" ceremony of a local official's house last year. I just had to do a lot of searching to even find that English term, because at 25 one doesn't necessarily know that many people who are building homes.
What I attended was the ridgepole-raising ceremony or 上棟式. We had lunch with the builders and, no surprises, there was mochi maki—throwing mochi to thank guests and for good luck. In the pictures you'll see a giant pancake mochi that had 500 yen inside. This is like how when you catch the bride's bouquet you are supposedly the next to get married, except in this case you're the next to build a house—and here's 500 yen to help you with that.
To come to the point of all this: I couldn't attend the actual housewarming on Thursday evening because I had to teach, but my colleagues and I ordered a nice houseplant which they took as a present. In true Japanese style the return present that I got was at least four times more valuable than my contribution to the the plant. But, since I'm totally in love with these deliciously porky bits already, I'm not complaining. I encourage you to look at more yummy pictures of Karari sausages からりソーセージ!