They'll ask you if you want it. You have to be in the room for them to start it (I believe that they can finish it for you if you do need to go in the middle of it)
You can put your things in there as an aid, but I believe that they do it with their stuff.
If they leave a photo in the room, do not press "Take away". It wont go into your photo list since it isn't your picture, but the furniture will be ok if you do that.