I think Luffy will be on the roof at the end of next chapter or the chapter after that.
Obviously Marco will carry Zoro there too so by 999 all of Kaido and Big Mom's opponent's will be up there.
The pace is increasing, I think chapter 1000 will be the 2 yonkos vs Luffy, Zoro, Kidd and Killer. Law will join later.
I hope we have a bit more pages for this event and some epic actions from both sides.
There is also the possibility that Oda end act 3 at 999 and shows us what's happening on the outside of Wano. It could also be epic, with BB doing whatever he was planning to, Marines vs schishibukai outcomes, Sabo's whereabout, maybe some new stuff and people hyping what's happening in Wano.