In the Chapter 1-1  Desireたいです is introduced. In this section, we will learn how a speaker try to draw some sympathy/empathy/agreement from a listener by adding ん  between  たいand です.  

This structure is only used in spoken situations.  Be careful with to whom you will speak this type of sentence.  You avoid using this structure when you are talking with a superior professionally since it can sound immature and whining. Keep it to your friends and colleagues in casual occasions.

In some cases, you can use it with people (even with strangers) when you want to imply that you are lost  and need a help.  For example, You are at a train station, and you cannot figure out  at a ticket vending machine how much your have to pay for a ticket to your destination.  Or you are lost on the street, and you want someone to help you show a way to your destination.  In such cases, you want to sound as if you desperately need a help. Here are commonly used phrases to seek for a help on the street, すみません。　ちょっと　おうかがいしたいんですが...　Sorry. I would like to ask you a question.(very polite)　すみません。　ちょっと　おききしたいんですが...  Sorry. I would like to ask you a question. (neutral)

Spoken:　私は日本で着物が買いたいんですが、着物は高いんで、浴衣を買うつもりです。 I want to (empathy) buy kimono in Japan but, since kimono is expensive, I intend to buy yukata.

Written:　私は日本で着物が買いたいですが、着物は高いので、浴衣を買うつもりです。　　

Note: んで is often changed to ので in writing, and it indicates a reason why you do something. 

私は日本で着物が買いたいので、他（ほか）のおみやげは買いません。Since I want to buy Kimono in Japan, I do not buy other souvenir (implying that Kimono is expensive and/or I cannot afford anything else but Kimono.)

This structure can be used this way with a hidden implications:

Spoken:　私はきものが欲しいんですが、お金が足りないんです...。　I want Kimono but I do not have enough money (the money is lacking).   You are implying your parents or your sugar daddy/mommy  おこずかいを少しください  Please give me some allowance.

Spoken:　私はラーメンが食べたいんですが、一人でラーメン屋に行きたくないんです。I want to eat Ramen but I do not want to go to a Ramen shop alone, You are implying your friend... 一緒に行きませんか。Could you go with me?  Or you are hoping your fiends to say "一緒にいきましょう。Shall I will go with you? or Let's go together.")

Spoken:　私は今寝たいんですが、ラジオの音がうるさいんです。I want to sleep now but radio is too loud.  (You are implying your housemate　静かにしてください。Please be quiet. Or you are hoping your housemate to say "Sorry, I will turn it down.)

Spoken:　私はとてもお腹がすいているんで、ビッグマックが食べたいんですが、最近ちょっと太り気味なんで... I am so hungry and want to eat a BigMac but I am a bit getting heavy lately...  The implication can be "so I better eat a salad or something less calorie.

Spoken:　晩御飯を食べましたが、今何か甘いものが食べたいんです。 I ate a dinner but I want to eat something sweet now.  You are implying...  Do you have something sweet for me? or Do you want to go out for a desert with me? etc.)

Spoken:　新しい車を買いたいんですが、もう２台もあります。(frequency/amount +も+ positive = as many as…)　ガレージにペースがないんです。　I want to buy a car but I already have as many as two cars so I do not have a space in the garage.  (Implication can be several things such as "So I am not buying another one." or "So I am planning to buy a small motor bike." Or (if you are talking to your next door neighbor who has much space around his home.  "Can I park at your space?" or you are hoping your neighbor to say you can park at their space.