A photo would help but with a finished attic it is a real posibility
that there is no roof ventilation or air gap inbetween the roof deck and
insulation. My neighbor has a cathedral ceiling their roof that is in
direct sun was trash after 7 yrs a 35 yr roof. Soffit vents and ridge
vent may or may not help, air still may not circulate. Are any areas in
complete shade that are ok. Look into it before you buy . An air gap
before the attic insulation was instaled and proper venting would have
cured it, if it is a venting air circulation issue. You dont want to pay
for a new roof every 10 yrs.