Should I attempt to remove about 1/3 of a roof rafter myself?

I just bought a foreclosed house and need to do some work in the back part of the house and to do so I'd sure like to have access to that part of the attic of which there is no access now. The back part of the house seems to be an addition. The original roof has the ridge beam running side to side and then they installed a ridge beam running perpendicular off that to cover the addition. When they did this they didn't cut a portion of the old roof out to give access to the attic over the addition. I'd like to cut out an access opening. I assume this would be similar to framing in a door where you sister in some jack[rafters], put in a header, and some cripple [rafters]. I'm not too sure what the configuration for the header should look like on these 2X8's or if I should attempt to do this myself? All this will be done with a permit and the city inspector's oversight. However, I'm not going to walk in to pull a permit and sound like an idiot, but on the face of it, it doesn't look overwhelming or outside of my capabilities. Any help will be appreciated. Thanks.