I'm finishing the interior of a garage that has prehung exterior doors installed. The door frames were sized for 2x4 studs but the wall framing is 2x6, leaving about a 3/4" gap between the inner edge of the door frame and the inner edge of the jamb studs and header.

Should I attempt a corner with the drywall here or would it be better to nail a piece of trim to extend the door frame which I can butt the wall's drywall up against? I wasn't planning on trim around the doors, but I guess that would hide any corner issues. Is there a standard way to handle this problem?

It's a garage - doesn't have to be living room quality but I'd like it to look finished.

 

The standard way to avoid that problem is to buy prehung doors that are 6 9/16 wide, which is what you usually want when you have a 2x6 wall, 1/2" sheathing, and 1/2" drywall. Adding jamb extensions on the interior of an exterior door is usually not the best option because it limits the swing of the door and the latch will usually scrape up the door extension unless you get a wide strike plate.

You also could have installed the 4 9/16" doors flush with the interior surface of the drywall... added the jamb extension to the exterior side of the jamb, and reinstalled the brickmould. The aluminum threshold could have had an aluminum threshold extension (an accessory) attached to it if it was one that is made to accept them.

Probably the best solution I could offer, since it's a garage, is drywall up to the rough opening, cutting it flush with the r.o. Then add some trim to the rough opening as an extension jamb, but rather than nailing it to the prehung door jamb... rip it down to the correct size so that it lines up with the OUTSIDE EDGE of the door jamb on all three sides. Nail it to the rough opening, shimming it out to meet the edge of the door jamb as needed. Then run a very fine bead of construction adhesive around the inside corner that is created. Finally, install a 1/2" x 1/2" quarter round into that inside corner to finish it off. This will help you leave enough space for the door to swing open a little wider... it will provide enough clearance so that your latch won't scratch the trim as the door comes closed, and you will still be able to use the standard strike plates that come with most door knob / deadbolt sets.

Then apply some casing to finish it off.

But if you want to try a drywall corner you can certainly do that. i'm a better carpenter than I am a drywall finisher, so I know which way I would choose. You'd probably want to shim the rough opening out before you apply the drywall (so that the reveal around the door is perfectly consistant at about 1/2" or so) and use a tear away l-bead against the door.