Make sure you drawn in scaled furniture. Once you account for "walkway" space your room won't be so "great".

16 ft ceilings should work ok. What is the ceiling height in the adjacent rooms?

9ft on the adjacent rooms

Ask your designer for some 3D color renderings so you may see the space as it will be built.

Consider asking for a plan review -- I see multiple things that might be improved.

I'd think of the great room as within the red box, and the blue as a hallway.

Vault just the great room, moving the fireplace and beams to center within this space.

Make sure you understand how the vault, and beams, will transition to the flat ceiling of the kitchen and dining. Details are important in achieving the rustic/cabin feel, and your designer needs to share this vision and know how to accomplish it.

butler's pantry /bŭt′lərz/

noun

1. A serving and storage room between a kitchen and dining room.

Piggybacking on PPF's comment of visualizing 3Ds and how the cathedral transitions to flat ceilings, also look at the interior elevations within the cathedral'ed room. For instance, the Foyer is open, but the corners of the opening do not align with any beams, and may create odd trapezoidal shapes above doorway openings or mess up homeowner's desires for strict symmetry. Also sometimes certain styles of houses want short wall returns at corners.

Yes, my first thought was to ask why you can't see visually inside the designed house on a computer?

Are there actual architects nowadays unable to provide this? I'd be really disappointed.

16’ is WAY too high for a nice warm people gathering spot. The actual usable space of that room is not made any better or bigger by having more room overhead than you have under foot. It’s an elevator shaft.

👆this comment just above. My first thought that was also that 16’ is plenty (PLENTY) high. Written as I sit on my couch in my vaulted 12’ family room. (This room size is 35’ x 26’.)

Random thoughts:

I think 16' is too high. That's literally double a standard-sized ceiling height.

In addition to the height, you must consider the details included in this ceiling -- you know the saying, the devil's in the details:

- Do you like a steep look (which can be severe) or something more moderate?

- Will the ceiling be white with beams or wood tone? They give a very different look.

- Will you have beams on the ceiling or tie-beams, or both?

- How will this room connect with the surrounding rooms?

- Will these beams be rustic or more finished?

- What about lights? Placed properly, they can really enhance a cathedral ceiling. Consider cove lighting around the edges or mood lighting that shines up onto the ceiling.

- What about windows? They're make-or-break items.

- Fireplaces are most often placed at the end of the cathedral ceiling /masonry to the apex of the ceiling. Have you considered placing yours on the exterior wall /flanked by glass doors?

You really need to see a visual representation of your architect's vision, as cathedral ceilings vary widely.