How to create method in runtime and add it to existing class

Question

I have a class like :

 public class OverTimeViewModel
    {
        public Guid uniqeid { get; set; }
        public string WorkType { get; set; }
        public int RequestDate { get; set; }
        public string RequestTime { get; set; }

    }

I want add Method like:

  public string Write(string message)
                    {

                            return message;
                    } 

is there any way to this by roslyn or codedom?