Plane.cs

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

[RequireComponent(typeof(MeshFilter))]
[RequireComponent(typeof(MeshRenderer))]
public class Plane : MonoBehaviour {

	[Range(2,100)]public int width = 10;
	[Range(2,100)]public int length = 10;

	[ContextMenu("Setup Mesh")]
	void SetupMesh () {
		int size = width * length;
		Vector3[] verts = new Vector3[size];
		Vector2[] uvs = new Vector2[size];
		Color[] colors = new Color[size];
		List<int> tris = new List<int>();

		for (int x = 0; x < width; x++) {
			for (int z = 0; z < length; z++) {
				int index = x + z * width;

				verts[index] = new Vector3(x, 0, z);
				uvs[index] = new Vector2(
					(float)x / (float)width, 
					(float)z / (float)length
				);
				colors[index] = Color.white;

				if (x < width-1 && z < length-1) {
					int above = x + (z+1) * width;
					tris.AddRange(new int[] {
						index, above    , above + 1,
						index, above + 1, index + 1,
					});
				}
			}
		}
		Mesh mesh = new Mesh();
		mesh.name = "Plane";

		mesh.vertices = verts;
		mesh.uv = uvs;
		mesh.colors = colors;
		mesh.triangles = tris.ToArray();
		mesh.RecalculateNormals();
		mesh.RecalculateBounds();
    
    		MeshFilter meshFilter = GetComponent<MeshFilter>();
		meshFilter.sharedMesh = mesh;
	}
}