public interface IPartShop { }

class Roof : IPartShop { }
class Floor : IPartShop { }
class Wall : IPartShop { }

public abstract class PartShopFactory
{
    public abstract IPartShop BuildPartShop();
}

public class RoofFactory : PartShopFactory
{
    public override IPartShop BuildPartShop()
    {
        return new Roof();
    }
}

public class FloorFactory : PartShopFactory
{
    public override IPartShop BuildPartShop()
    {
        return new Floor();
    }
}

public class WallFactory : PartShopFactory
{
    public override IPartShop BuildPartShop()
    {
        return new Wall();
    }
}
static void Main(string[] args)
{
     PartShopFactory pathShopFactory = new RoofFactory();

     IPartShop roof = pathShopFactory.BuildPartShop();

     Console.ReadKey();
}