Gonna be helping a friend build a new house after a complete burnout.
His ceilings are going to be 9'. what is the standard procedure for
drywalling 9' walls?

We built our own house and had walls varying from 8' to 15'. I personally
prefer to hang sheets vertically. This ensures all edges are supported by
framing, and all edges on the wall are tapered for smoother joints (you
would end up with butt joints if your walls are longer than 16', which we
had many). True, it will be a bit more work to tape, but I've always done
it this way and haven't found it to be a big deal.

Another advantage to hanging sheets vertically is you can use standard off
the shelf drywall 4x8, 4x10, or 4x12, cut to the height of your wall. It
wastes a little drywall, but can save over special order fees.

If you're working alone, hanging sheets vertically usually allows you to
use smaller sheets which means less weight to carry.

If you do choose to hang sheets horizontally, and can't find wider sheets,
my preference would be a 1' band at the top or the bottom, so you can
maintain tapered edges. Tapered edges allow much smoother joints, and
you'll really appreciate the difference if you have to mount a cabinet to
the wall or something (no "bulge" in the wall from the butt joint).

I put a 1' band at the top of the wall when we remodeled my in-laws
bathroom. I had to climb the ladder to do the ceiling corners anyway, so it
was easy to do the seam near the top of the wall at the same time. I would
normally cut down 10' sheets and hang them vertically, but in this case it
was more efficient to hang the sheets horizontally (less waste).

Anthony