Re: changing value of cost parameter in all wall element in my project

Hi thanks for your solution but i still have problem i repair as your solution

 foreach (Element e in new FilteredElementCollector(doc).OfClass(typeof(WallType))){

Parameter cost = e.LookupParameter("Cost");
               using (Transaction t = new Transaction(doc, "param"))
                    {

                        t.Start();

cost.Set(50);

 t.Commit();
                    }

}

but i have this error in my revit