Since I walked in the sun, I was thirsty.
Should I say like below? :
1. I'm dying for a long, cold drink.
2. I'm dying for a cold drink for long.
3. I'm dying for a cold drink for long time.
Please comment. Thanks.
"Long" in the context of your sentence 1 is not about a long time. It means that the drink is in a long (tall) glass so it contains a lot of liquid. Your sentences 2 and 3 use the word long in a different sense. If you want to say that you have wanted a drink for a long time, you can say that, but it is not the same as wanting a long drink.