I haven't yet found an easy button to click in the stairs tool that allows this, it would be nice to have some more options in the stair tool. We usually just draw a series of stairs with a platform.
1. Draw the lower portion of stairs up to the height or the platform
2. Create a platform using slabs
3. Create one side of the upper portion starting at the height of the platform and mirror it over the platform to get the T-shape
Use slabs for the stair treads and the roof tool for the bottom of the stairs. Trim the roof object to the slabs using the "Solid Elements Operation" tool.