When I tried to build a wall around Outpost Zimonja I had a ton of issues because the ground is so hilly. I could not get the walls straight and even. But I saw folks here saying this:
QUOTE(hazmick @ Mar 14 2017, 12:45 PM)

Concrete foundations are the way to go with uneven ground. The concrete clips through the ground to give you a nice even base for walls.
QUOTE(TheCheshireKhajiit @ Mar 14 2017, 12:47 PM)

That's pretty much how Khajiit does it; puts a concrete foundation (the cheaper one in "wood" structure floors) to make it even. Plus you can then build rooms or a pavilion into your walls so it's not all wasted space.
QUOTE(TheCheshireKhajiit @ Mar 14 2017, 02:28 PM)

QUOTE(Cain @ Mar 14 2017, 11:55 AM)

I think it's doable with concrete walls, too. You can snap them, and then slide them up or down to make sure there are no gaps underneath. That way you get walls, without the foundations. Takes a lot of patience, though.
After playing with it, that could serve! You can set up the first part of your wall to the desired height and then put the rest of them together until you run into significantly higher ground. If you have gaps under the wall where the ground dipped you can put a concrete foundation as Hazmick suggested. This fills the gap and you can utilize the floor for a storage room or something! Will have to do something different for higher ground though.