how to hang 200lb chandelier?
Check with the manufacturer of the fixture. They should have some design parameters.
If they are modern day conventional residential roof trusses, I recommend contacting a mfg of same.  See what they say.  
I personally would take a 3' piece of standard #2-and-better 4x6 lumber, free of flaws, lay it perpendicular across the top side of two trusses to use as your main support.  Drill and screw in place. 
A standard 4-square metal box with a round mud ring will support the fixture.