First way is to flip your character. But its very complicated, because requires some custom gravity implementation.
Maybe this one will be useful for you.
Another way is to rotate whole map, or specific locations in map, but this requires dynamic setup for all objects and lightning. In this case, I think, it is better to generate map procedurally.
Hello all,
I’ve started learning UE4 about 2 months ago and the following is one of the experiments I want to imply in a project of mine.
I have a game where you control a cube in a rolling motion around the map (the objective is irrelevant to this question).
I want to add a mechanism where you can flip the map 90 degrees (then walls will be floors). How do you think is it best to approach this mechanism? and is it possible if the map is big enough? Can I specify the pivot point around which the actors will all rotate? just tell me everything you think about such a mechanism.
Thank you 
I flipped the character but didn’t need to make custom gravity (I don’t render gravity in my game I just add the few mechanics of gravity that I need manually to the actors). Had some problems with every node that had World (location, rotation, offset) but managed to replace those with a slightly different code that used local (location, rotation, offset).
Thank you