public abstract class Request
{
   public class Parameters
   {
       //Threre are no members here
       //But there should be in inherited classes
   }

   public Request()
   {
       parameters = new Parameters();
   }

   public Parameters parameters;
}

Two questions:

1. How do I make it so I can add stuff to the constructor but the original constructor will still be executed?

2. How do I make it so the subclasses can add members to the Parameters class?