用英语讲好中国故事：空中楼阁 Castle in the air
In the Western Han Dynasty, there was a rich landlord in Taiyuan City. He was very wealthy but rather dull-witted, so he was often ridiculed.
西汉时期，在太原城有一个土财主。他钱财众多，但头脑愚笨，所以常常被人嘲笑。
One day, he went to visit another landlord surnamed Zhang. He saw a newly built three-story house of Mr. Zhang, which was tall and bright. He was extremely envious and thought: I am as rich as him. He has such a beautiful house, but I don't. This is really unreasonable. I also want to have such a house.
有一天，他到另一位姓张的财主家去做客。他看到人家新盖好的一座三层楼的房子，又高大又敞亮，心里特别羡慕，想着：我和他一样富有，他能有这么漂亮的一座楼，可我却没有，这实在太不像话了，我也得有这样一座楼。
The next day, he called the artisans and asked, "Do you know who built the house of Mr. Zhang in the neighboring village?"
第二天，他就把工匠们找来，问道：“你们知道邻村张老爷家的楼是由谁盖的吗？”
The artisans said, "It was us." The landlord was very happy when he heard this and said, "Great! Then build me another three-story house exactly the same as that one!"
工匠们回答说：“正是我们盖的。”土财主听了特别高兴，说道：“太好了！那你们就照那个样子再给我盖一座一模一样的三层楼！”
The artisans began to build the house as he ordered. A few days later, the landlord came to the construction site to inspect. He looked around for a long time and was very puzzled. Then he asked, "What are you doing?"
工匠们按照他的吩咐，开始动工建房。过了几天，土财主来到工地查看。他这边看看，那边瞧瞧，看了好半天，心里十分疑惑，便问道：“你们这是在做什么？”
The artisans said, "We are building the three-story house as you ordered." The landlord hurriedly said, "No, no. I only want the top floor. I don't want the bottom two floors. Take them down quickly."
工匠们说：“我们按照您的吩咐，正在盖那座三层楼房呢。”土财主赶忙说：“不对，不对。我只要最上面的那一层，下面的两层都不要，赶快给我拆掉。”
The artisans laughed loudly after hearing this and said, "We can't build only the top floor. You'd better do it yourself!"
工匠们听完后哈哈大笑，说：“只要最上边那层，我们可不会建，您还是自己来吧！
This idiom comes from "The Parable of the Three-Storeyed House" in "Sutra of Hundred Parables". Its original meaning refers to a pavilion hanging in mid-air. Now it is often used to describe unrealistic theories, plans or fictional things. It can also be used to describe being brilliant and insightful.
这个成语出自《百喻经·三重楼喻》，原本的意思是指悬挂在半空中的楼阁。现在常用来形容脱离实际的理论、计划或者虚构出来的东西，也能够用来比喻高明且通透。