https://openacs.org/forums/message-view?message_id=33870 https://openacs.org/forums/message-view?message_id=62086
Also, Jerry Asher (theashergroup.com) has a problem set solution that seems to be nice (I had no luck getting logged in there).
As I see from discussions room reservation package should be what I actually need. Don Baccus also mentioned about it in his reply. I will try to port it to 4.6 and see how it possible to join with Calendar package.