Tags and Layers Enums Builder for Unity3D

example of Layers.cs

//This class is auto-generated, do not modify (use Tools/TagsLayersEnumBuilder)
public abstract class Layers {
	public const string Default = "Default";
	public const string TransparentFX = "TransparentFX";
	public const string IgnoreRaycast = "Ignore Raycast";
	public const string Water = "Water";
	public const string UI = "UI";
	public const string Camera = "Camera";
	public const string Characters = "Characters";
	public const string Floor = "Floor";
	public const string Sprites = "Sprites";
	public const string Terrain = "Terrain";
	public const string Squads = "Squads";
	public const string Selectable = "Selectable";
	public const string Obstacles = "Obstacles";

	public const int DefaultMask = 1;
	public const int TransparentFXMask = 1 << 1;
	public const int IgnoreRaycastMask = 1 << 2;
	public const int WaterMask = 1 << 4;
	public const int UIMask = 1 << 5;
	public const int CameraMask = 1 << 8;
	public const int CharactersMask = 1 << 9;
	public const int FloorMask = 1 << 10;
	public const int SpritesMask = 1 << 11;
	public const int TerrainMask = 1 << 12;
	public const int SquadsMask = 1 << 13;
	public const int SelectableMask = 1 << 14;
	public const int ObstaclesMask = 1 << 15;

	public const int DefaultNumber = 0;
	public const int TransparentFXNumber = 1;
	public const int IgnoreRaycastNumber = 2;
	public const int WaterNumber = 4;
	public const int UINumber = 5;
	public const int CameraNumber = 8;
	public const int CharactersNumber = 9;
	public const int FloorNumber = 10;
	public const int SpritesNumber = 11;
	public const int TerrainNumber = 12;
	public const int SquadsNumber = 13;
	public const int SelectableNumber = 14;
	public const int ObstaclesNumber = 15;
}

example of Tags.cs

//This class is auto-generated, do not modify (TagsLayersEnumBuilder.cs)
public abstract class Tags {
	public const string AIOrder = "AIOrder";
	public const string Camera2D = "Camera2D";
	public const string CameraMan = "CameraMan";
	public const string Dangerous = "Dangerous";
	public const string Debug = "Debug";
	public const string EditorOnly = "EditorOnly";
	public const string EnemyStatsBar = "EnemyStatsBar";
	public const string Finish = "Finish";
	public const string Fire = "Fire";
	public const string Formation = "Formation";
	public const string GameController = "GameController";
	public const string Ground = "Ground";
	public const string HUDPanel = "HUDPanel";
	public const string Item = "Item";
	public const string MainCamera = "MainCamera";
	public const string MatchTimerLabel = "MatchTimerLabel";
	public const string Obstacles = "Obstacles";
	public const string Player = "Player";
	public const string PlayerSkillPointsBar = "PlayerSkillPointsBar";
	public const string PlayerSpawningPoint = "PlayerSpawningPoint";
	public const string PlayerStatsBar = "PlayerStatsBar";
	public const string RangedAttack = "RangedAttack";
	public const string Respawn = "Respawn";
	public const string SelectedSquad = "SelectedSquad";
	public const string Skill = "Skill";
	public const string SkillButton = "SkillButton";
	public const string SkillLabel = "SkillLabel";
	public const string Smelly = "Smelly";
	public const string SquadPosition = "SquadPosition";
	public const string SquadSelector = "SquadSelector";
	public const string SquadSpawningPoint = "SquadSpawningPoint";
	public const string Unit = "Unit";
	public const string Untagged = "Untagged";
}

TagsLayersEnumBuilder.cs

#if UNITY_EDITOR
using UnityEngine;
using System.Collections;
using UnityEditor;
using System;
using System.IO;
using System.Text;

public class TagsLayersEnumBuilder : EditorWindow {
	[MenuItem("Edit/Rebuild Tags And Layers Enums")]
	static void RebuildTagsAndLayersEnums() {
		var enumsPath = Application.dataPath + "/Code/Enums/";

		rebuildTagsFile(enumsPath + "Tags.cs");
		rebuildLayersFile(enumsPath + "Layers.cs");

		AssetDatabase.ImportAsset(enumsPath + "Tags.cs", ImportAssetOptions.ForceUpdate);
		AssetDatabase.ImportAsset(enumsPath + "Layers.cs", ImportAssetOptions.ForceUpdate);
	}

	static void rebuildTagsFile(string filePath) {
		StringBuilder sb = new StringBuilder();

		sb.Append("//This class is auto-generated, do not modify (TagsLayersEnumBuilder.cs)\n");
		sb.Append("public abstract class Tags {\n");

		var srcArr = UnityEditorInternal.InternalEditorUtility.tags;
		var tags = new String[srcArr.Length];
		Array.Copy(srcArr, tags, tags.Length);
		Array.Sort(tags, StringComparer.InvariantCultureIgnoreCase);

		for (int i = 0, n = tags.Length; i < n; ++i) {
			string tagName = tags[i];

			sb.Append("\tpublic const string " + tagName + " = \"" + tagName + "\";\n");
		}

		sb.Append("}\n");

#if !UNITY_WEBPLAYER
		File.WriteAllText(filePath, sb.ToString());
#endif
	}

	static void rebuildLayersFile(string filePath) {
		StringBuilder sb = new StringBuilder();
		
		sb.Append("//This class is auto-generated, do not modify (use Tools/TagsLayersEnumBuilder)\n");
		sb.Append("public abstract class Layers {\n");
		
		var layers = UnityEditorInternal.InternalEditorUtility.layers;

		for (int i = 0, n = layers.Length; i < n; ++i) {
			string layerName = layers[i];
			
			sb.Append("\tpublic const string " + GetVariableName(layerName) + " = \"" + layerName + "\";\n");
		}
		
		sb.Append("\n");
		
		for (int i = 0, n = layers.Length; i < n; ++i) {
			string layerName = layers[i];
			int layerNumber = LayerMask.NameToLayer(layerName);
			string layerMask = layerNumber == 0 ? "1" : ("1 << " + layerNumber);
			
			sb.Append("\tpublic const int " + GetVariableName(layerName) + "Mask" + " = " + layerMask + ";\n");
		}

		sb.Append("\n");
		
		for (int i = 0, n = layers.Length; i < n; ++i) {
			string layerName = layers[i];
			int layerNumber = LayerMask.NameToLayer(layerName);
			
			sb.Append("\tpublic const int " + GetVariableName(layerName) + "Number" + " = " + layerNumber + ";\n");
		}
		
		sb.Append("}\n");

#if !UNITY_WEBPLAYER
		File.WriteAllText(filePath, sb.ToString());
#endif
	}

	private static string GetVariableName(string str) {
		return str.Replace(" ", "");
	}
}
#endif

I use this instead and just manually update it.

using System;

namespace Legend
{
    public static class Layer
    {
        public const int Default = 1;
        public const int TransparentFX = 1 << 1;
        public const int IgnoreRaycast = 1 << 2;
        public const int UserLayer3 = 1 << 3;
        public const int Water = 1 << 4;
        public const int UI = 1 << 5;
        public const int UserLayer6 = 1 << 6;
        public const int UserLayer7 = 1 << 7;
        public const int Ground = 1 << 8;
        public const int Projectile = 1 << 9;
        public const int Enemy = 1 << 10;
        public const int Player = 1 << 11;
        public const int BlocksPlayerMovement = 1 << 12;
        public const int Pickup = 1 << 13;
        public const int EnemyProjectile = 1 << 14;
        public const int ProjectileIgnored = 1 << 15;
        public const int FlyingPlayer = 1 << 16;
        public const int Debris = 1 << 17;
        public const int Walls = 1 << 18;
        public const int PlayerInvulnerable = 1 << 19;
        public const int Animal = 1 << 20;
        public const int Zones = 1 << 21;
        public const int Environment = 1 << 22;
        public const int NoSpawn = 1 << 23;
        public const int NPC = 1 << 24;
        public const int Building = 1 << 25;
        public const int UserLayer26 = 1 << 26;
        public const int UserLayer27 = 1 << 27;
        public const int UserLayer28 = 1 << 28;
        public const int UserLayer29 = 1 << 29;
        public const int Item = 1 << 30;
        public const int UserLayer31 = 1 << 31;
    }
}