I start at the top and have the tongue down for nailing.
It is easier to nail this way, and the ridge is guaranteed to be even.
There is no need for the tongue to be up on an interior wall. Exterior is different where weather can be an issue.
If you are using an 18 gauge pin nailer, use two nails at each rafter location. Nail them at a slight angle 'sideways' (about 15 degrees). A 15 gauge would need only a single nail.
Cut the groove edge from the first ceiling to match the combined roof angle and the cut the second piece to butt into it and have the same exposure.
Prestained and prefinished is the way to go...
If you need further info, let me know and I'll post a drawing.
Check your measurement to the wall edge every couple of feet and adjust the joint tightness to keep the line running straight.
I've done a few square miles of ceiling this way. No issues with them.