The man on Jay's roof.

Long story short, the movie's script is trash. The rules are constantly rewritten. So because the director thought a shot of a naked man standing on a roof would be scary, that's why it's there. Forget the fact that "It" is supposed to be constantly following, now it's going to pose for the camera.

The concept that was said in the movie is that It is always walking. You can drive far and that gives you time to think of a plan but It will ultimately catch up to you if you stay in one place too long. The guy on the roof had just caught up to her and was probably going in through the window but now has to walk to the pool which is why they are laying around the pool waiting for It to get there.

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The rules were not rewritten, because nobody in the film knows the rules. The first guy has a couple observations but he doesn't know what it is or what its rules are.

It´s said indeed that IT is intelligent... so taking that into mind we can infer that the previous actions into Jay´s house made the creature take a smarter choice than break into her door or windows, and instead climb on her roof and make a surprise fall into the room through their balcony or whatever acces is easier. A naked man through the window by surprise would make a higher impact on her mind and could probably paralize her with fear. In my opinion, of course.

It seemed to take damage temporarily, if it jumped off the roof it would have stumbled and as they were about to drive away in a car it probably decided jumping was pointless.

Why do people so frequently get told to read the book on a movie database?