Wall slopes/diagonal walls

[gtrx]

I've been mapping for AC for a little while, but I still don't know how to do "wall slopes" as seen here with ac_urban:
https://drive.google.com/file/d/1NnMYcha...sp=sharing
https://drive.google.com/file/d/1rBiPLrB...sp=sharing

[Mousikos]

https://assault.cubers.net/docs/mapediti...ml#corners