using System;

public class Program

{

    public interface IHasCeiling

    {

        decimal? Ceiling { get; }

    }

​

    public abstract class CalculationMethodParameter : IHasCeiling

    {

        public decimal? CeilingQuantity { get; set; }

​

        decimal? IHasCeiling.Ceiling => CeilingQuantity;

    }

​

    public class MaMethodeParam : IHasCeiling

    {

        public decimal? Ceiling { get; set; }

    }

    public class JourTravaille : CalculationMethodParameter { }

    public static void Main()

    {

        var calParam = new MaMethodeParam { Ceiling = 12 };

        Console.WriteLine(((IHasCeiling)calParam).Ceiling);

        var jourTravaille = new JourTravaille { CeilingQuantity = 99 };

        Console.WriteLine(((IHasCeiling)jourTravaille).Ceiling);

    }

}