Water stain on ceiling after thunderstorm

[netaaron]

A day after the thunderstorm I noticed a stain in the ceiling. I went into the attic and right above where the stain was I saw this cutout. I'm assuming the water got thru from the roof and leaked onto the ceiling from that cutout. Everywhere else is dry. Any suggestions on how I should approach this? Get a professional or is this a do-it-yourself job?

[pushkins]

The cut out is for ventilation purposes when one roof covers over sheathing, it's very very common in fact probably should be larger than it is (depending on the size of the roof area on the other side).
Regardless of the cut out the issue is shingle leakage, look for water stains on the underside of the sheathing and see if you can follow them back to the source. Often it can be as simple as a popped nail of a shingle not sealing down on the asphalt strip.
If you can get on the roof safely check to make sure all the shingles in the area of the suspected leak are not loose or the tabs lift up (they should be stuck down) remember leaks on roofs almost always originate higher up the roof than where the stain is.