I have an antique restored interior door with a transom for which I have to make my own jamb due to the height of the side jambs (big boxes sell only 80" door jambs). Should I
A) assemble the jamb and hang the door on it outside the rough opening before fitting it in (basically pre-hang it myself) or
B) assemble the pieces of jamb inside the rough opening?
I am inclined to think A because how else do I know how much shimming I will need. However, one problem I see with that is how to assemble 1x planks of the jamb at right angles around the door and set the hinges in correct spots. It seems like I would need a firm frame to support the composition.