I am needing advice and you guys are some of the smartest on the web.
As you know I have a 30x30 building with 10 foot ceilings. The trusses
are 4 feet apart so I am not sure I can put a drywall ceiling. I plan
on drywalling the walls.

My thoughts are this, either a suspended ceiling with the 2x4 tile or
I thought of using the soffit material like that is used on the roof
of my porch. (The kind without vent holes). When I figured up the cost
for both they were very similar. (Not cheap).

We have suspended ceilings at work and when new they look good but
whenever there is a roof leak or something they get ugly looking
stains on the tiles and the tiles are not cheap. Also, I am a little
worried about the humidity messing with those tiles over time. Also,
when I read the literature, it said to plan on 20 hours of labor to do
a suspended ceiling for a 9x14 room! Since I have to work myself, I
cant image how long it would take to do a 30x30.

So, I have gone back and forth on the issue. Do you guys see any
problem with soffit material? My thought is to use 1x4’s nailed on the
bottom of the trusses about every 2-4 feet to help minimize sagging.
Will the soffit still sag? Will it be possible to keep the rows of
soffit straight and how do I go about doing that. (With a chalk line?)

Above whatever type ceiling I use will be clear plastic vapor barrier
with unfaced r-30 fiberglass insulation.

One caveat is I can see sometime in the future needing to get in the
ceiling to run wire or whatever. Hopefully someday to run a central
heat/air unit but that may be a long time from now.

Also, on another note, we have had torrential rains last night. I had
drops of water on the center of the floor. I crawled in the ceiling
and the best I can tell is it is blowing in from the top “ridge cap”
that is on the center of the roof. I assume this is used for
ventilalation?

Anyhow I really appreciate your help!