I have no idea take some pics of the actual space . Arches plunked into aspace for no reason are just silly . Waht do you need to store there . Get the plan right before the contractor starts being the designer . I need a to scale floor plan to actually understand what you are doing some pics too . That is how you get help here

Agree with @Lyn Nielson on keeping things lower contrast in the small space - would be nice to recess cabs into the walls where possible

Can you inert shelving between the framing so it doesn’t stick out and is flush with wall?

A cabinet in front of glass will look odd, but a cabinet in front of a full height wing wall won't.

Do you have a floor plan? Hard to understand exactly how much space you have with your pictures.

Thank you for all of your input. Cabinets cannot be recessed because of plumbing and electrical. We do have a lot to store--as I said it is a 480 square foot cabin so we will not have much other storage inside. The arch would mainly be so the cabinet would be in front of the arch wall instead of glass.

Our architect's floor plan is no longer accurate because we expanded the bedroom and closet into the bathroom (we realized the bathroom was taking up too much square footage for such a small home), so this is the best I have. It is proportionally accurate.

And here is the current space:

Install a partial wall there. Place a linen tower there. Better storage, better meshing of technical construction details.

That "current" demo condition, has walls, a window, an entry and can be MEASURED. Can be shown in a sketch, with a dimension, feet and inches for every piece of solid wall, the window and the entry door...all have their OWN dimensions.

You provide, upload, neatly . boldly even on graph paper, and you get help.

Even better, mark up what you changed, on the original arch plan for the entire 480 sq feet. and add that as well.

You still haven't said what you need to store. What's on the other side of the shower wall?

KISS Put a full height wall to the right of the shower up to the beam. I am not sure the arch makes sense unless the rest of the place is Tuscan? Put a cabinet butting up to that wall and make it full height-floor to ceiling so you have a lot of storage. Hang towels on the outside of the doors to the cabinet so make sure the surface can handle the moisture.

The shower is oversized for a 480 sq ft home. You need to allocate space based on time spent in the space. IT also has more expensive glass than needed. If you want the larger shower size, then reduce the glass by adding a wall to the right, and that's where you will hinge a door. That allows you to do tall 21" cabinets right up to that wall.

There is a TON of wasted space in the whole thing. Someone is terrible at space planning.