You need a compound mitre saw for this.

Consider making the forward facing gable the full width of the red structure. You could make the peak of the gable higher and put your chimney on the left (taller wall) side.

I am using a compound miter saw and I am committed to this design as I already have everything done besides the crown molding roofline and chimney. My question is around getting that joint I circled just right. I cut my test pieces as a 24 degree but when I join the two sides the one running up to the peak won’t sit flat on the wall.

My husband is good at this stuff and even he is scratching his head! He says get the angled one correct and just keep chipping away at the straight piece leaving it long till you get it right, and good luck!

What is the spring angle of your crown molding?

45

Are you cutting your molding standing up against the fence with the top edge leaning against the fence?

Or laying flat with the top edge against the fence?

Against the fence

When you say you have a 48-degree roof angle, do you mean if you cut your crown @ 48-degree angle at the peak where the rake meets the rake the molding will confirm to the roof slope?

If not you using the wrong angle.

The angle where the rake meets at the peak is 48. I cut two test pieces at 48 degrees for the peak to confirm.

You will need a bevel compound miter to make that lower cut and you would have to be making that cut by laying the molding flat on the miter saw because you will need a crown molding miter angle to be 1.33 degrees and a crown molding bevel angle of 23.96 degrees to get that cut

both with top edge molding against the fence.

Thank you! I will do a couple test pieces with those angles

Burt, if cutting both moldings @48 degrees at the peak your rafter slope is @ 42 degrees. If that's the case, the miter saw setup would be different.

Laying the molding flat on the miter saw the top of the molding being against the fence, the miter angle should be 1.15 degrees, and the saw blade bevel angle @ 20.97 degrees.

search "crown moulding vaulted ceiling" Ron Paulk had a good video on it, extremehowto another.

As you can see I got the peak and the right side all set. I mirrored the bottom left angle to the right side but now I am stuck. I am thinking I need to redo this left side but what angle should I cut it so that the straight piece that I need to install to the left lines up perfectly? Please note that this bottom angle is at 90 degrees, if that helps.

This is your cut just instead of 140 use the angle that you have...from 180 deduct the angle you have and divide it by 2 = your miter cut for both pieces...like in the picture

I see on one of your pictures you have an angle 132.5 so you take 180-132.5=47.5/2=23.75 which is your miter cut for both pieces. If you want the molding to die into the pine (1 sided cut only) 47.5 is the miter on the molding.