Yes, otherwise there is no topping out ceremony - why do you think there are so many flat roofs?
That is of course nonsense. The real consequences of skipping a topping out ceremony are: - No gifts, - Bad luck, - 20 years of bad sex. I actually know builders who held neither a topping out ceremony nor (a few months after moving in) a housewarming party. And they are alive! And they are doing well! But a bad construction manager and a stupid company should not stop you from doing what you want. Is the topping out ceremony important to you? Then celebrate it (the way you want to celebrate it, not your construction manager)! If not, then don't bother...