adding more shipping options to my shipping.cs file

Hello All,
I have a class file called shipping.cs , where i calculate my ground shipping like below

public class GroundShipping : Shipping
{
    #region members

    private double _ShippingCost;

    #endregion

    #region properties

    /// <summary>
    /// gets or sets the ground shipping charges associated with the order
    /// </summary>
    public override double Cost
    {
        get
        {
           // shipping cost for different dollar amount
            if ( _ShippingCost < 0 )
            {
               
                if ( _O ...