The roof does look pretty flat and the overhang doesn't look like much so if that is the case, it shouldn't be overly heavy.
If this is the case and it were me, I would use either 6x6 or lally columns and run them at basically a 45degree angle, attaching to the roof line in 2 different places and lagging them to the steel step structure in some way. Then id tear an entire side down, all 4 stories and rebuild it properly, using steel supports.
Finish one side, then start the other side.
If you look closely at the picture, you can see the roof line is actually starting to sag, as it isn't getting enough support in those 4 places. So first thing id do is build temporary supports on the stairwell and then id remove the wood beams, and install a lvl or steal beam that runs 1/2 the length of the building and center it then use again solid beams, be in lally columns or steel beams to hold the new beam up. This alone would help support the roof 100 times better while rebuilding everything else.