If you have or want to purchase a biscuit jointer they do a nice job of keeping your extensions sturdy and lined up with the jambs.
Door jamb not flush with drywall.
While preparing a door frame for casing we notice the drywall is not flush with the door frame.
However you can certainly use it to create a 2 tone look as well where the door panel is different from the wall color.
If not i think your best option is going to be to build the extensions proud of the wall and then bring them down flush with a power planer or belt sander.
When it comes to frameless doors flush primed door panels are the top choice for many designers due to their versatility.
Watch a simple way to build and install your own wood trim that also solves a common problem with drywall that extends too far past door and window jambs.
The drywall is shaved to allow the casing to sit flat on the wall and on the frame.
2 basic time taken.
In other words the jamb is not at a perfect 90 degree angle to the door and the door hits the jamb not allowing it to completely close.
This is caused by over shimming the door jamb opposite the hinge side.
Flush primed door panels are ideal when you want your wall and door color to be the same.
The casing door and window frame moldings should be mounted parallel to the drywall not canted in.
Nail through the shims and then trim the shims flush to the outside edge of the casing.