Hi, I am a 3d generalist & game developer with expertise in various software including unity.
I have ready your requirements & based on my expertise I will write a unity editor tool that you can use to procedurally create walls around terrain & add thickness to them as required, since I will write your script as a unity "editor tool", it will be accessible from unity editor menu bar & with a custom window of it's own, making the tool easier to use.
Also I will provide some additional benefits such as
1. Proper code optimization
2. Fully commented out code
3. Create system as a proper unity editor tool instead of a single script
4. PDF documentation
Feel free to contact me & to discuss any further details.