On an earlier post you saw how to create a stair using multiple copies of a thread component. On this post you'll see how to improve on that model.
To draw the stair stringers, pick the Line tool and draw the edges as shown below.
Now use Push/Pull to extrude the face and make it into a Component. Then use Move(press and release Ctrl) to copy it to the other side.
Now let's make the thread so as to make the "open riser". Enter the thread component edit context by double-clicking one of the threads. Then use Push/Pull pushing up the bottom face to get the desired thickness.
To conclude, select all the parts to create a single stair component.
Cross posted from sketchuptips.wordpress.com