Could not really comprehend from your sketch. If the whole space is for one function, then best not to have the sliding door.

If the extension room is to be use as a bedroom and the existing room as a study, then have the sliding door since you said that you want to reduce the aircon coverage when sleeping. You can have the sliding door open to allow the cool breeze from the aircon from the other room when using the study.

I wouldn't say that a 12' x 11' room is small. It will depends on your ID and room layout.

If cost is not an issue, you could opt to take down the wall and replace the whole opening with folding sliding door. They could be closed to create 2 separate rooms and open up to have a large room. You have flexibility

If cost is a concern, then put up a timber frame sliding door.
When the door is fully open, you will not see the door as it is hidden behind the wall.

This post has been edited by kelvyn: Sep 5 2011, 09:29 PM

cheapest alternative