I have a unique situation in which I need to reach a ~21′ sloped ceiling peak.  After trying every type of step ladder, extension ladder, and multi-position ladder I have access to, I believe I have found a solution.  However, I’m not sure if what I want to do is common practice.  

I would struggle to describe the design of the house in words, so I’ve attached a crude Sketchup drawing to supplement my description.  Apologies in advance for any confusion. 

The drawing shows 2 sets of baker scaffold setup on the main floor (less outriggers, which I will have!).  The 3rd set will span a pony wall; one buck on the 1st and 2nd sets, the other buck on the 2nd floor.  I will also have guardrails, which I will attach, if needed or if possible.

I made the 2nd floor and left stair wall transparent, so the scaffold is visible.  

I need to finish installing a beam at the ridge (shaded green) and cleanly cut-in the ceiling and wall paint (shaded orange).

This is the only solution I’ve found which gives safe access to the areas.  This is a finished, lived-in home.  If it were not, I would be attaching cleats to the walls or building a temporary deck on the stairs.  But the finished walls, carpeted stairs, etc, prevent me from doing so.  

I would love to hear your thoughts on this setup.  Is it possible (other than in space)?  Is it safe (relatively speaking)?  Is there another way?

Thank you in advance.