After the rafters, we started on the facia around the top of the house. The facia boards give the sheathing and siding something to bump up against along the top edge, as well as provide a base for the roof air gap (hopefully this will make more sense later).
At first, we installed this facia, but it turned out to be too thin (1x3), so we took it all down (after installing the sheathing) and replaced it with 2x4s instead.
After we got the facia up, we started on the sheathing. This took UNBELIEVABLY long! Making sure everything was square, level, and flush was infuriating, basically the entire time. We got so frustrated with it that there are parts that definitely aren't square. There are gaps. There are bits we had to trim off with the sawzall because they hung over the edge. This was the first time in this project where we got so fed up with making sure it was was perfect, that we ended up just plowing through with a "good enough!" kind of attitude. And really, it is good enough. The gaps and crooked edges don't really matter structurally, and they'll be covered first by house wrap, then siding.
We drilled screws every about every 8 inches on the studs, except around the edges of each plywood board, where we drilled every 6 inches. We also made sure to caulk underneath along the studs as well. The ol' "glue and screw".