Can bethesda make a tool for building at the settlements, so you can even the ground a bit.
If you want to place a wall, it is almost impossible to put it the way you would liked.
It does not have to be like in zootycoon, but just to make it a little more workable.

Use foundations. They're big concrete blocks or wooden poles with floor on top that can clip into terrain and create a flat floor to work with.

yea foundations or look up a clipping tutorial

Foundations. You can move them up and down by using the E key and scrolling. Not sure what it is on a controller. (E is used to quick loot and activate on pc).

yeah foundations are for that

Hey OP, check out this vid...first tip:

https://www.youtube.com/watch?v=8CR8nOTDhh8

This solved over 99.99999% of my foundation problems when trying to build on uneven ground.