If your question is whether you can span 25 ft. with 2x8 x 16" o.c. ceiling joists, the short answer is no.
Not even if you tripled each joist.
2x12 @ 12" o.c. would be a much better choice.

If your question is whether (4) 2x6 will work as a beam, the answer is HECK NO.
Have somebody size a (much taller) LVL beam for you.

 

Welcome to the forum, Robert.

Can you give us a sketch of your plan for this space? Even if you can’t do it on a computer you could draw it by hand, take a photo with your phone, then upload it. I think what you’ve described is a 40’ X 25’ space divided into five 25’ long spaces by four 2x8s (but those spaces aren’t of equal width), then you plan to run 2x6s perpendicular to those on 16” centering. Is that correct?

Will the space above the ceiling be open for someone to walk around on, so the structure that you’re building would need to support that weight as well as drywall? Any other weight, like insulation, or storage?

Chris

 

Yes sir-

 

You need a structural engineer to size an adequate beam for what it has to support. My ballpark estimate to support a floor at that span would be a fairly big LVL or a decent sized steel wide flange beam. If you don't need to clear span that 25' (you can add a post or posts to shorten the span) the beams can be much smaller.

Apologies; I misread the OP. My advice about getting a SE still applies, though.

 

there are two basic ways of construction of a steel building. One is inside and one is out side.
Outside the columns are exposed inside .inside the columns are outside
All of the engineering for your building was done based on holding itself up. Not for a bunch of extra materials.
I suggest that you contact the desider of your building and see what they recommend.
Putting wood inside a metal building creates a lot of other issues.

Here is an early pic of mine, 70 x 30 x 15 tall. NO wood, no fire blocking, no termites,
The columns stay exposed.

 

If you do not have engineering sign-off you will likely not get insurance. At least not honestly and if you fib to insurance they will be off like a prom dress in case of accident. For your peace of mind please contact your building vendor and seek their blessing.

 

Thank You