I want to put a pergola on my flat roof but am not sure if it's possible to construct one safely. My roof is a wide open flat surface built to be enjoyed as a rooftop deck with tufflex deck layer. I want to attach the posts directly to the roof (that seems the most secure) but I don't think that is possible due to compromising the integrity of the roofing layer (I assume it would require redoing the entire roof to create brackets that would be more properly sealed from leaking). On the other hand I'm not sure how to calculate if concrete blocks are enough to prevent it from flying away which would be catastrophic as it would fall 3 stories. Unfortunately there is no structure I can attach it to other than the ~4ft walls around the roof that are capped with a metal sheet.
Has anyone done this or do you have ideas on if it can be done safely? I was originally planning to just attach the pergola to concrete blocks but I'm worried about gusts of wind and have no insight on if this is safe or what amount of weight is needed to secure it. For the pergola frame I plan to use bamboo due to its light weight and strength: my idea is that the center of mass would be much lower using bamboo vs a traditional hardwood or even an aluminum frame. It would also put less load on the roof itself, but I sacrifice potential stability as cedar pergolas are 5x the weight I believe.
In summary, is it possible to construct a pergola on a flat roof safely given my constraints (roofing material, no obvious part of the house to attach it to, etc)?
Edit: The roofing material is actually tufflex
Edit2: Added a more representative picture due to commentary