Here I will give more info about turntables in SCARM - hope it will be useful 
SCARM has a dedicated library statement for representing turntables in the plan and for O-scale there are two turntables already included in Atlas-O-2 and Atlas-O-3 libraries - select some of these libs and scroll to the bottom of the tracks list in selection panel to see the turntables.
If there are more manufacturers that are making ready-to-use turntables, let me know and I will search for the TT parameters to prepare the appropriate libraries for them.
If you want to make a custom turntable and represent it in SCARM track plan, you can use the method of Moonman or edit some of the libs and add your own turntable inside. The libraries are plain text files and can be edited with Notepad. Let me know and I will provide additional info about the statement syntax in the libraries.
@Ace: Thank you, Ace If you or somebody else wish to share own SCARM layouts on O-gauge track plans section of SCARM Layouts and Track Plans site, send the .scarm file with some short explanation to me and I will do the rest 
Mixy
