Heads up: I just realized that there will no doubt have to be terraform alone the outer wall, so I recommend we avoid actually building those roads for the time being. Be a shame to have to just dig it up again!
Once I figure out what the wall will look like (thinking a consistent Y level for most of it) we can start terraform for the wall and road.
I was thinking we could do something like you see in old Asian fortresses, where the wall is slightly up on a hill, with the road on top. Like illustrated in this professional drawing I did:
I was thinking the same... I'll just leave the outer road until at least a section of wall is done.
To raise the ground up around the whole circumference of the outer wall will take a lot of dirt and work! (But then you seem to like projects like that!)