Second Floor L Stairs?

Yes, tested the build and the stairs work fine all the way up. It also is weather proof - you'll face problems with roofing, that's why the flat roof and chimney in an odd place. The stair landing squares causes that the roof has to be placed on 3rd floor above them and for the same reason normal roof doesn't lay down neatly as the squares have the effect on all the squares next to them... so 2 squares affect the area of 3x4 squares which the regular roof can't cover.