This is a paid asset, but now you can download the “Fence, Wall and Hedge Builder” for FREE, Please keep in mind this package is provided only for learning purposes or to be able to test before buying the product, NOT FOR COMMERCIAL PURPOSES.
For more detail this asset from the Unity Asset Store: Click Here
Fence, Wall and Hedge Builder v3.5
Fence, Wall and Hedge Builder Lets you quickly place walls in you game, using a user-friendly UI from within the scene editor or the inspector, Select from a list defined wall types and then select the style of that type.
Just place the wall prefab into your scene and then click Add wall button, Then use the dropdown list to select the type of wall (BrickWall, Hedge, Panel wall, etc) and then pick the style of the wall (Large, Medium, small and unkept or aged).
You can also add extra features to the wall, like gaps, gates, arches.
Version 1.1: Added a drop corners to ground option.
Version 2.0: You can now add more that one gap feature to a wall.
Added new hole style gaps to walls with size and offset.
Added new Temporary wall types.
Version 2.1: Fix the UVs project for walls and hedges, Add new wall gap feature HoleSquareArch, Added new Thin Wall styles, Removed the 1 width limit for the new gap features, Fix some bugs with the StoneFeet on the Temporary Fences
Version 3.0: Connected corners are shaped to make each section of the wall join.
Version 3.1: Added the Option to use different material for each side of the wall. Added new materials
Version 3.2: Fix a small bug with the stretching textures at the end of the walls
Version 3.3: Added two new Wall types. Castle Walls and Mounds
Example and documentation can be found Here