One more inspiration on this site .
It do approximately what You want but You need to generate 3D objects not only flat.
So, could be a very long way.
I suggest You to start with more common stairs and than to add country specific restrictions.
Also You must decide the approach:
1. Do an plugin, or
2. Do an separate application.
While You don't need too much from SH3D You could choose the 2.