There are many opinions of
There are many opinions of how the Miraculous staircase was built. I believe that he first built the base of the stairs. He did this by warping the wood in sections by soaking it and then slowly applying pressure. Also I think that he was using a softer wood to make it easier to warp and position the boards. He would continue to do this until he got all the way to the top, using supports to hold it up until he got all the way.
Once at the top he would secure it and support it by putting beams from the floor to the stairs. After securing the base to the top, he would carve the step-like pattern into the thick base until he reached the top. After carving, he would put faces on all the tops so it would look nice and not all cut up. Finally, he would polish, smooth, and paint the wood down until it looked perfect.
That is how I think the miraculous staircase was built.