How can I make some tiles on a mesh higher up than others?

For the record, I'm using C#.

I'm completely lost with what I should do here - I've got code that can generate a plane mesh of arbitrary size, but I don't know where to go from here. I want to be able to make it so that some tiles (made of two triangles at this point) are higher than others. Given a multidimensional array of X,Z coordinates, with a binary flag for whether or not the tile is a wall, how can I make the code I have raise some tiles up in the air to form walls? I'm primarily experienced in making 2D games, and this is the first time I've ever attempted procedural generation in a 3D game, and one of the first 3D projects I've ever worked on.

I hope I'm making sense. If not, here's a glorious MS Paint illustration:

Just imagine you're looking at a cross section of a level from the side.

Below is the code I have:

using UnityEngine; using System.Collections; using System.Collections.Generic;

public class Generate : MonoBehaviour {

 public int sizeX = 50;
 public int sizeZ = 50;
 public float tileSize = 1.0f;

 
 // Use this for initialization
 void Start () {
     BuildMesh();
 }
 


 public void BuildMesh() {
     int numTiles = sizeX * sizeZ;
     int numTris = numTiles * 2;
     List<int[]> map = new List<int[]>();

     //Create a map of all tile coordinates, with binary (0, 1) for whether or not the tile in question is a wall.
     for(int xi = 0; xi < sizeX; xi++){
         for(int zi = 0; zi < sizeZ; zi++){
             int[] xz = new int[3];
             xz[0] = xi;
             xz[1] = zi;
             xz[2] = Random.Range (0, 1);
             map.Add (xz);
             Debug.Log ("Tile " + xz[0] + ", " + xz[1] + " mapped!");
         }
     }
     
     int vSizeX = sizeX + 1;
     int vSizeZ = sizeZ + 1;
     int numVerts = vSizeX * vSizeZ;
     
     // Initialize the arrays that will hold our mesh data.
     Vector3[] vertices = new Vector3[numVerts];
     Vector3[] normals = new Vector3[numVerts];
     Vector2[] uv = new Vector2[numVerts];
     
     int[] triangles = new int[numTris * 3];
     
     int x, z;

     for(z=0; z < vSizeZ; z++) {
         for(x=0; x < vSizeX; x++) {

                 vertices[ z * vSizeX + x ] = new Vector3( x*tileSize, 0, -z*tileSize );
                 normals[ z * vSizeX + x ] = Vector3.up;
                 uv[ z * vSizeX + x ] = new Vector2( (float)x / sizeX, 1f - (float)z / sizeZ );
                 
                 
             
         }
     }
     Debug.Log ("Vertices done.");
     
     for(z=0; z < sizeZ; z++) {
         for(x=0; x < sizeX; x++) {
             int squareIndex = z * sizeX + x;
             int triOffset = squareIndex * 6;
             triangles[triOffset + 0] = z * vSizeX + x + 0;
             triangles[triOffset + 2] = z * vSizeX + x + vSizeX + 0;
             triangles[triOffset + 1] = z * vSizeX + x + vSizeX + 1;
             
             triangles[triOffset + 3] = z * vSizeX + x + 0;
             triangles[triOffset + 5] = z * vSizeX + x + vSizeX + 1;
             triangles[triOffset + 4] = z * vSizeX + x + 1;
         }
     }
     
     Debug.Log ("Triangles done.");
     
     // Now, we create a mesh and then use the data we just generated to populate it.
     Mesh mesh = new Mesh();
     mesh.vertices = vertices;
     mesh.triangles = triangles;
     mesh.normals = normals;
     mesh.uv = uv;
     
     // Then we fill the mesh filter and collider with the mesh we just created.
     MeshFilter mesh_filter = GetComponent<MeshFilter>();
     MeshCollider mesh_collider = GetComponent<MeshCollider>();

     
     mesh_filter.mesh = mesh;
     mesh_collider.sharedMesh = mesh;
     Debug.Log ("Mesh Done.");
     

 }
 
 

}