The custom stair tool is not part of the default workspace, you have to edit…
Vectorworks Tip 426 – Creating a Straight Stair With the Simple Stair Tool
For concept design, I think the simple stair takes a lot of beating. It’s easy to use, it’s very quick to use, and it gives you some pleasing results without too much bother with settings. Because it is a simple stair, you have very limited graphic and handrail abilities, but remember the conceptual design, you don’t want to have too many options.