In the spirit of "teach a man to fish", let's work it out:
Assume truss spacing is 2' on center
Assume the ceiling "joist" and "rafters" are 2x6's (conservative; 2x4's might work).
Assume the other truss chords are 2x4's.
"Ceiling joist" truss member is 40' long.
The two "rafters" together are about 45' (based on a 4-in-12 pitch, and assuming some overhang).
We'll assume all the other truss members together total 40 lineal feet.
So we have 85 lineal feet of 2x6 and 40 lineal feet of 2x4.
Assume Douglas fir or Southern yellow pine at a specific gravity of 0.5 giving a density of about 30 pounds per cubic foor.
Dimension of 2x6 is 1.5 by 5.5 inches; this gives 1.5 * 5.5 * 12 or 99 cubic inches per foot. This gives us a wood volume of 0.057 cubic feet per foot.
This gives us a weight per lineal foot of 1.7 pounds, which seems reasonable for a 2x6.
Similarly, our 2x4's weigh about 1 pound per foot.
1.7 pounds per foot x 85 feet = 146 pounds 1.0 pounds per foot x 40 feet = 40 pounds
Total 186 pounds per truss. We'll add another 14 pounds for the metal plates or other gussets and use a budgetary figure of 200 pounds per truss.
One note of caution is that trusses like this are very weak against forces perpendicular to the plane of the truss. They cannot even support their own weight if lifted flat, and will come apart if you try. The truss manufacturers have very specific requirements for how to attach and use lifting slings. Furthermore, because trusses are designed to bear weight only on their ends, a 40 foot long truss may require a spreader bar and two separate slings, even if otherwise handled vertically.
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