Need help with trim around a giant door

I have a large multi panel glass door (37 ft) which is suspended from 3 beams, and I want to add trim around it (simple flat trim) but I am having trouble with finding a method that works by reducing the gaps to something that can be caulked. The ceiling has a variance of about 3/8". It is not tapered, but wavy, so if I put flat stock up there it will have many large gaps. Oh, and the beams are twisted too. I have learned a lot here at the creek, but I am still not a carpenter. Any thoughts are appreciated!

Pic#1 - The desired outcome: Simple flat trim
Attachment 473992

Pic #2 - Cross section of the parts:
Attachment 473993

Pics 3&4 - Photos of the door attachment, hard to see distances:
Attachment 473994 Attachment 473996

cut the width of the long piece 3/8 + a touch wide, then tack it up to the beam. use a compass set at 3/8 + a touch in between the point and the pencil. scribe the trim keeping the compass vertical. remove from the wall, use a belt sander or similar to get to your line and keep a little back rake on it, so the outside edge is slightly higher than the inside edge.

This is what I would do in a higher end home or business.

if its a commercial client, I would probably just hang the trim and caulk it to the celling with tape on both sides of the caulk joint, let the painter worry about it.

If you want wood trim there, you might need to scribe it to the ceiling. I’m not sure that’s the best look for a modern door, however. Why not bring the drywall down over the beam and terminate it with a j bead? Seems like a cleaner way to trim out that door.

What’s the offset between the beam and door channel? From your drawing it looks to be about 3/4”.

I assume you’re not wanting the beam to be highlighted (show)? What’s the “knuckle” sticking out of the beam close to the ceiling in the last photo?

Pull a mason's line from one end to the other as tight as you can get it, and tighten it some more on a plane where you want the back of the jamb extension. Cut individual spacers to fit above the line, leaving a half of a hair of daylight between it, and the line. DON'T PUSH THE LINE. Nail your jamb extension through those.

I keep boxes full of these spacers, in about 20 different variations in thickness.

Once you get that set, follow Adam's method to fit the casing.

Scribing tight and/or caulking will highlight the waves. A vertical drywall return with j bead or floating the ceiling with mud to eliminate the waves will be a cleaner look.

Thanks for al the input folks. I was planning for wood trim painted the two house colors, but now I am considering a drywall return (haven't done that before).

@Kevin - I suck too bad at drywall mud to flatten the ceiling, so with a drywall return I figure I am doing the same thing only a different material. Is the highlighting of the waves due to a color change between the two surfaces? In other words, if I just do a vertical piece of drywall and paint it green (compared to the toupe ceiling), will it still highlight the waves? Will keeping it ceiling color help conceal them?

@Eric - The drawing is not to dimension, just a kwik eyeball. The backset from the door channel from the trim is about 1/2". Hiding the beam is job #1, and the "knuckle" is one of several bolts holding that 4x6 "beam" to the glulam.