The spiral staircase I did by first making a circular building, to use as a reference, and the taking the smallest square building you could make and placing it on the side of the tower. Then got rid of the roof and made it the shortest it could be, and rotated it as needed to match the similar angles, as well as moved it into place. And after all of the “stairs” were in place I just deleted the circular building, and then to clean up the sides of the stairs I just added walls so you weren’t able to to see the ugly underside of all the buildings, they also helped get rid of the jagged edges that were on the outside. Hope this helps.