Many people do not like the custom stair tool and it has been removed from the default Vectorworks workspace. In order to find it you will need to customise your workspace, locate the custom stair in the legacy category and add it to your own workspace. The Custom Stair works differently than the main Vectorworks stair tool in that it works on the concept of parts. You add a flight, then you add a landing, the new and another flight, then you can add another landing or winder, then you can add another flight, and so on. That makes the stair extremely flexible, much more flexible than the standard stair tool.