I created a test room on chat, but I can't see how to delete it.
Only moderators can delete rooms at the moment.
We're still working out the details on room-level actions.
Provided that the room had less than 15 messages or fewer than 2 users that posted, it will get deleted automatically if it is inactive for 7 days. You thus don't have to do anything (other than not post) to get it deleted.
If you need to ensure deletion of a room you own, and you have at least 1,000 chat reputation, you could set the chat room permissions to Gallery, to make sure that others don't post and keep it alive.