If you have a room or deck that's a little complex and took awhile to do and you need to duplicate it one or more times you can save the room to My Library then go in and grab it and place again where you need it at to save building it again. Then when your finished with it just delete from My Library.
Lets say you build a deck on your house.
Now if you want this deck again on the second floor of the house you can go to the trouble to build it again or save it to My Library by selecting the room and use Save Room, give a name and save it.
Now that it's save just open My Library and grab the room. Sense it was just saved it should be the first on there and select Place Room
Place the room where you want it.
And drop in place
Need another one just go grab it from My Library again