To elicit a sentence or phrase like this, I'd first build up a scenario in which the target language is appropriate. Some miming or simple picture drawing can help a lot.
What's the scene? Well, I want to open the window. Why? Maybe I'm hot. But there are other people in the room. Am I just going to open the window? Maybe I should ask them if it's OK. What question am I going to ask?
Eliciting is much easier if you break it down into several parts. Elicit the scenario from your students, piece by piece where necessary, and then they'll more easily understand what target language you're trying to introduce - and if they don't know the TL, you'll have made the teaching easier by giving them some context.
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