Voxel C# source problems.

So, I'm working on a small project to make a browser game that's like Minecraft. I'm working along side YouTube instruction videos and some of the project is turning out good, but I'm currently facing two problems.

First, The z positioning walls will not draw. Here's my code:

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 [RequireComponent (typeof(MeshFilter))]
 [RequireComponent (typeof(MeshCollider))]
 public class Chunk : MonoBehaviour {
     public int width = 20;
     public byte [,,] map;
     
     protected Mesh mesh;
     
     protected List<Vector3> verts = new List<Vector3>();
     protected List<int> tris = new List<int>();
     protected List<Vector2> uv = new List<Vector2>();
     
     protected MeshCollider meshCollider;
     
     // Use this for initialization
     void Start () {
         meshCollider = GetComponent<MeshCollider>();
         map = new byte[width, width, width];
         for (int x = 0; x < width; x++)
         {
             for (int z = 0; z < width; z++)
             {
                 map[x, 0, z] = 1;
                 map[x, 1, z] = (byte)Mathf.RoundToInt(Random.value);
             }
         }
         
         mesh = new Mesh();
         GetComponent<MeshFilter>().mesh = mesh;
         
         Regenerate();
     }
     
     // Update is called once per frame
     void Update () {
     
     }
     
     public void DrawBrick(int x, int y, int z, byte block)
     {
         Vector3 start = new Vector3(x,y,z);
         Vector3 offset1, offset2;
         
         if(IsTransparent(x, y - 1, z))
         {
             offset1 = Vector3.left;
             offset2 = Vector3.back;
             DrawFace(start + Vector3.right, offset1, offset2, block);
         }
         if(IsTransparent(x, y + 1, z))
         {
             offset1 = Vector3.right;
             offset2 = Vector3.back;
             DrawFace(start + Vector3.up, offset1, offset2, block);
         }
                 if(IsTransparent(x - 1, y , z))
         {
             offset1 = Vector3.up;
             offset2 = Vector3.back;
             DrawFace(start, offset1, offset2, block);
         }
         if(IsTransparent(x + 1, y, z))
         {
             offset1 = Vector3.down;
             offset2 = Vector3.back;
             DrawFace(start + Vector3.left + Vector3.up, offset1, offset2, block);
         }
         
                 if(IsTransparent(x, y, z - 1))
         {
             offset1 = Vector3.right;
             offset2 = Vector3.up;
             DrawFace(start + Vector3.forward, offset1, offset2, block);
         }
         
         if(IsTransparent(x, y, z + 1))
         {
             offset1 = Vector3.left;
             offset2 = Vector3.down;
             DrawFace(start + Vector3.up + Vector3.back, offset1, offset2, block);
         }
 
     }
     public void DrawFace(Vector3 start, Vector3 offset1, Vector3 offset2, byte block)
     {
         int index = verts.Count;
         
         verts.Add (start);
         verts.Add (start + offset1);
         verts.Add (start + offset2);
         verts.Add (start + offset1 +offset2);
         
         tris.Add (index + 0);
         tris.Add (index + 1);
         tris.Add (index + 2);
         tris.Add (index + 3);
         tris.Add (index + 2);
         tris.Add (index + 1);
     }
     
     
     public bool IsTransparent(int x, int y, int z)
     {
         if ((x < 0) || (y < 0) || (z < 0) || (x >= width) || (y >= width) || (z >=width)) return true;
         return map[x,y,z] == 0;
     }    
     
     public void Regenerate(){
         verts.Clear();
         tris.Clear();
         uv.Clear();
         mesh.triangles = tris.ToArray ();
         for (int x = 0; x < width; x++)
         {
             for (int y = 0; y <width; y++)
             {
                 for (int z = 0; z < width; z++)
             {
                 byte block = map[x,y,z];
                 if (block == 0) continue;
                     
                 DrawBrick(x, y, z, block);
             }
         }
     }
         
     mesh.vertices = verts.ToArray();
     mesh.triangles = tris.ToArray();
     mesh.RecalculateNormals();
     
     meshCollider.sharedMesh = null;
     meshCollider.sharedMesh = mesh;
 }
 }

It's a C# script named 'Chunk.' The blocks generate, I can walk on them, but some of the walls will not generate. What directions do I need to set within the z - 1 and z + 1 areas?

Second, I made a file named 'PlayerIO' and I have to add a Chunk file (a C# one) to make the rest of it work with the tutorial. I'm able to add everything, but it won't let me add my chunk file! Here's the image:

When I drag the Chunk C# file into the Chunk section, the 'No Access' sort of cursor popsup, and it won't let me add it.

Does anyone know a solution to these problems? Thank you!