Tommy does pre-hung doors (if video still around).
Note: When marking from bottom of shortest jam, allow
7⁄16 for tile if floor unfinished. When the door is in
place, these marks on door jam edge and wall opening will line up. There should
ample and even crooked space at the top under the header; this will be corrected
(hidden) by casing.
* If the opening slants out of plumb, nothing can be done: just follow it matching jam
with studs and sheetrock thickness. The door cannot be used to correct that in the way it can
across the other axis.