Create a sortable list with this re-usable class on the fly.

SortableList.cs

using System.Collections;
using System.Collections.Generic;
using UnityEditor;
using UnityEditorInternal;
using UnityEngine;

namespace Adnc.Pathfinding2D.Utility {
	/// <summary>
	/// Usage example:
	///   [CustomEditor(typeof(MyBaseClass))]
	///   public class MyBaseClassEditor : Editor {
	///     private SortableList buildTasks;
    ///
	///	    void OnEnable () {
	///		  buildTasks = new SortableList(this, "mySerializedProp", "Title of list");
	///	    }
    ///
	/// 	public override void OnInspectorGUI() {
	///       DrawDefaultInspector();
	///       serializedObject.Update();
    ///
	///		  if (buildTasks.list != null) {
	///			buildTasks.list.DoLayoutList();
	///		  }
    ///
	///		  serializedObject.ApplyModifiedProperties();
	///	    }
	///   }
	/// </summary>
	public class SortableList {
		public ReorderableList list;

		public SortableList (Editor editor, string property, string title) {
			var prop = editor.serializedObject.FindProperty(property);
			if (prop == null) {
				Debug.LogErrorFormat("Could not find property {0}", property);
				return;
			}

			list = new ReorderableList(editor.serializedObject,
				editor.serializedObject.FindProperty(property),
				true, true, true, true);

			list.drawElementCallback =
				(rect, index, isActive, isFocused) => {
					var element = list.serializedProperty.GetArrayElementAtIndex(index);
					rect.y += 2;
					EditorGUI.PropertyField(
						new Rect(rect.x, rect.y, rect.width, EditorGUIUtility.singleLineHeight),
						element, GUIContent.none);
				};

			list.drawHeaderCallback = rect => { EditorGUI.LabelField(rect, title); };
		}
	}
}