I'm in the process of rehab'ing a single story brick structure that has
seen years of abuse and neglect. The floor is in need of leveling and I
intend to sister the floor joists to achieve this. There is a large
window (approx. 8' x 5') in the back wall and the top of the window
"frame" is a 6"x8" piece of timber running the 8' width. Over time,
stress from the weight of the back wall & roof has taken its toll on
this piece of wood and it has now taken on a sort of tilda (~) shape.

The sagging roof joists need to be jacked up and the brickwork in the
back wall corrected. My question is simple. Does it make any difference
in which order I perform the aformentioned tasks?

Should I level the floor, install new subfloors then jack up the roof?
This would put a good deal of downward stress on the newly sistered
joists. The sistered joists *should* be sturdy enough to avoid knocking
the floor out of level again.

Should I jack up the ceiling first and place the stress on the original
unreinforced joists (they're 100+ yr old 2x8's)? I'm afraid this may
worsen their current condition.

Does it make any difference or am I just being paranoid?

thanks,
-josh