Do the cast members of SNL write the scripts themselves?
About 10/90%.. There is a large group of writers who generally (according to ex-SNL alumni) file into a large room with a huge oval conference table and just sit there and fire off ideas (such as Patton Oswalt [not an SNL writer] said “How about Midnight in the Olive Garden of Good and Evil”), they all mull it over and eventually come up with some sketches. Most of them are -not- cast members, but a handful are, included especially because they have a better knowledge of how audiences may receive the ideas and how to shape them. For the most part, though, the whole writing process is done by -writers- as the actors have SMTW off, do an experimental rehearsal Thursday, settle on and practice sketches on Friday, do a Dress Rehearsal early Saturday in front of an audience where the weak sketches are cut, and then perform. The actors simply don’t have enough time to participate in the writing process.