IdlingQueueService is a class to run actions in the Idling Revit event in a queue.

IdlingQueueService.cs

using Autodesk.Revit.UI;
using System;
using System.Collections.Generic;

namespace RevitAddin
{
    /// <summary>
    /// IdlingQueueService
    /// </summary>
    public class IdlingQueueService : IDisposable
    {
        private readonly UIControlledApplication application;
        private Queue<Action<UIApplication>> queue;

        /// <summary>
        /// IdlingQueueService
        /// </summary>
        /// <param name="application"></param>
        public IdlingQueueService(UIControlledApplication application)
        {
            this.application = application;
            this.application.Idling += Application_Idling;
            this.queue = new Queue<Action<UIApplication>>();
        }

        /// <summary>
        /// Add <paramref name="action"/> to run in <see cref="Autodesk.Revit.UI.UIApplication.Idling"/>
        /// </summary>
        /// <param name="action"></param>
        public void Add(Action<UIApplication> action)
        {
            this.queue.Enqueue(action);
        }

        /// <summary>
        /// Application_Idling
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void Application_Idling(object sender, Autodesk.Revit.UI.Events.IdlingEventArgs e)
        {
            var uiapp = sender as UIApplication;

            if (queue.Count != 0)
            {
                queue.Dequeue()?.Invoke(uiapp);
            }

            if (NeedToDispose) Dispose();
        }

        #region Dispose
        private bool NeedToDispose;
        public void Dispose()
        {
            NeedToDispose = true;
            try
            {
                this.application.Idling -= Application_Idling;
            }
            catch { }
        }
        #endregion
    }
}