建造者模式：一步步完成複雜任務

using System;
using System.Collections.Generic;

/// <summary>
/// 三明治產品
/// </summary>
public class Sandwich
{
    /// <summary>
    /// 麵包種類
    /// </summary>
    public string Bread { get; set; }

    /// <summary>
    /// 起司種類
    /// </summary>
    public string Cheese { get; set; }

    /// <summary>
    /// 蔬菜配料
    /// </summary>
    public List<string> Veggies { get; set; } = new List<string>();

    /// <summary>
    /// 醬料
    /// </summary>
    public string Sauce { get; set; }

    /// <summary>
    /// 顯示三明治內容
    /// </summary>
    public void Display()
    {
        Console.WriteLine($"三明治配料：麵包({Bread})、起司({Cheese})、蔬菜({string.Join(", ", Veggies)})");
    }
}

/// <summary>
/// 建造者介面
/// </summary>
public interface ISandwichBuilder
{
    /// <summary>
    /// 添加麵包
    /// </summary>
    void AddBread();

    /// <summary>
    /// 添加起司
    /// </summary>
    void AddCheese();

    /// <summary>
    /// 添加蔬菜
    /// </summary>
    void AddVeggies();

    /// <summary>
    /// 取得完成的三明治
    /// </summary>
    Sandwich GetSandwich();
}

/// <summary>
/// 義大利風味三明治建造者
/// </summary>
public class ItalianSandwichBuilder : ISandwichBuilder
{
    private Sandwich _sandwich = new Sandwich();

    public void AddBread() => _sandwich.Bread = "義大利麵包";
    public void AddCheese() => _sandwich.Cheese = "莫札瑞拉起司";
    public void AddVeggies() => _sandwich.Veggies = new List<string> { "番茄", "羅勒", "洋蔥" };

    public Sandwich GetSandwich() => _sandwich;
}

/// <summary>
/// 素食三明治建造者
/// </summary>
public class VeggieSandwichBuilder : ISandwichBuilder
{
    private Sandwich _sandwich = new Sandwich();

    public void AddBread() => _sandwich.Bread = "全麥麵包";
    public void AddCheese() => _sandwich.Cheese = "素食起司";
    public void AddVeggies() => _sandwich.Veggies = new List<string> { "生菜", "番茄", "小黃瓜" };

    public Sandwich GetSandwich() => _sandwich;
}

/// <summary>
/// 指揮者，負責掌控建造過程
/// </summary>
public class SandwichDirector
{
    public Sandwich Construct(ISandwichBuilder builder)
    {
        builder.AddBread();
        builder.AddCheese();
        builder.AddVeggies();
        return builder.GetSandwich();
    }
}

using System;

class Program
{
    static void Main(string[] args)
    {
        var director = new SandwichDirector();

        // 製作義式三明治
        var italianBuilder = new ItalianSandwichBuilder();
        var italianSandwich = director.Construct(italianBuilder);
        italianSandwich.Display();

        // 製作素食三明治
        var veggieBuilder = new VeggieSandwichBuilder();
        var veggieSandwich = director.Construct(veggieBuilder);
        veggieSandwich.Display();
    }
}