From my experience stairs need a square free at the top of them for doors as the door takes up a square and so do the stairs so the stairs won't connect. You could try building a square outwards from the wall and the door that is already there and that should allow the new bit of wall you want to add to connect straight with the door wall bit and would stop the stairs being raised when moving them out. If you use the full room tool and knock out the walls afterwards to make the platform it seems to have less clipping errors than the platform tool and wall tool, it might just mean that the stairs are out a square against the main wall though. 🙂