Wow. Was this problem disclosed (previous owner's disclosure form)....and what about the inspection report??? Hopefully you knew about this problem before you bought. For example, are there more than 2 layers of asphalt roofing (VERY HEAVY) up there?
I hope I'm wrong...but doesn't sound like a cheap fix to me. Best of luck...and keep us updated.
You will sister a new member along side the broken one and securely nail them together for the full length of the repair (6-8 inches apart in 2 staggered rows). The repaired area generally needs to overlap a minimum of 48” – 60” each way centered over the break and the new wood must be of the same size, species, and grade of wood as the original truss.
Like K2 I also would check into the disclosure clause as well as any inspection reports. Any additional loading added to the roof after the initial construction would also be a concern.