void HandleCheckoutElementsRequestTooLargeException(Document doc)
{
   FilteredElementCollector collector = new FilteredElementCollector(doc);
   ICollection<ElementId> rooms = collector.WherePasses(new RoomFilter()).ToElementIds();

   try
   {
      ICollection<ElementId> checkoutelements = WorksharingUtils.CheckoutElements(doc, rooms);
   }
   catch (Autodesk.Revit.Exceptions.CheckoutElementsRequestTooLargeException)
   {
      IEnumerable<WorksetId> worksets = rooms.Select(elemId => doc.GetWorksetId(elemId)).Distinct();

      TaskDialog dlg = new TaskDialog("Elements can't be checked out")
      {
         MainInstruction = $"You are trying to check out a large number of elements. Instead check out the following {worksets.Count()} worksets:",
         MainContent = string.Join(", ", worksets),
      };
      dlg.Show();

      TransactWithCentralOptions twcOptions = new TransactWithCentralOptions();
      ISet<WorksetId> worksetsCheckedout = WorksharingUtils.CheckoutWorksets(doc, worksets.ToHashSet(), twcOptions);

      TaskDialog.Show(
            title: "Worksets are checked out",
            mainInstruction: $"{worksetsCheckedout.Count} worksets are checked out.");
   }
}

Private Sub HandleCheckoutElementsRequestTooLargeException(ByVal doc As Document)
    Dim collector As FilteredElementCollector = New FilteredElementCollector(doc)
    Dim rooms As ICollection(Of ElementId) = collector.WherePasses(New RoomFilter()).ToElementIds()

    Try
        Dim checkoutelements As ICollection(Of ElementId) = WorksharingUtils.CheckoutElements(doc, rooms)
    Catch __unusedCheckoutElementsRequestTooLargeException1__ As Autodesk.Revit.Exceptions.CheckoutElementsRequestTooLargeException
        Dim worksets As IEnumerable(Of WorksetId) = rooms.[Select](Function(elemId) doc.GetWorksetId(elemId)).Distinct()
        Dim dlg As TaskDialog = New TaskDialog("Elements can't be checked out") With {
    .MainInstruction = $"You are trying to check out a large number of elements. Instead check out the following {worksets.Count()} worksets:",
    .MainContent = String.Join(", ", worksets)
}
        dlg.Show()
        Dim twcOptions As TransactWithCentralOptions = New TransactWithCentralOptions()
        Dim worksetsCheckedout As ISet(Of WorksetId) = WorksharingUtils.CheckoutWorksets(doc, worksets.ToHashSet(), twcOptions)
        TaskDialog.Show(title:="Worksets are checked out", mainInstruction:=$"{worksetsCheckedout.Count} worksets are checked out.")
    End Try
End Sub