I do not understand the issue just replace the tub with a shower of coures I am guessing since you have provided no infoa st height pf ceiling where the tub is.

We feel the issue is that the bathroom is taking up too much floor space in the room.

So this will be an office and a guest room ... so you must keep the tub /shower. If you were to remove the tub, it'd hurt your house's value /resale. Thoughts:

- Changing to a shower doesn't save you any space. You must have 30" in front of the toilet, and 8'6" is about as narrow as you're going to successfully build a two-sided bathroom. You don't have space to move the tub to the end of this bathroom, even if you go with a narrow shower. And if you could do any of these things, it'd be big money to save inches.

- If you're changing the bathroom vanity, I'd like to see something a little wider ... even a guest bathroom needs storage for towels and extra TP.

- If you need more storage, you could add a shallow piece of furniture (vintage china cabinet?) outside the bathroom door ... you have space on the landing.

Since you really can't lose any square footage in the bathroom, you might turn your attention to maximizing organization in the guest room:

- With the slanted walls, is a Murphy bed a possibility? A pull-out sofa?

- If you're going with a bed, make it a queen or even a full-sized bed. Guests don't NEED a luxuriously large bed.

- Maybe scootch the bed over into the corner (so it "backs up to" the tub) and go with a single night table on the outside. Not ideal, but -- again -- guests don't NEED full-time amenities.

- Go with a small desk, etc. for the office. Consider "building in" a desk under the eaves.

Make the vanity bigger and change it to a shower other than that nothing is wrong with the layout.

This is as small as you can get while still being usable. You don't gain anything by turning the tub into a shower and shrinking it. Anything smaller than 36 X 48" for a shower is uncomfortable to use. If this is a bathroom for a guests, they would find a small sink with no counterspace frustrating. If you really don't need a shower here, turn it into a half bath.

Who is going to be using the bathroom? What is the purpose of this room? Why isn't 12 X 15' large enough for the intended purpose? Since you are using an architect I think you need to trust that this is the minimum dimension unless you haven't correctly conveyed your requirements. They are thinking about the practicality of getting furniture up there, so you are already ahead of some people.

How big is the bedroom needed IMO the bathroom is as small as it can be and I have no info as to why you need this huge space for a guest room

You could easily have a good size shower with a seat and a larger vanity.

Can you show a section through the space that accurately shows the sloped ceiling, particularly at the toilet fixture? Something like this:

Not sure how feasible to move toilet where vanity is, back of the toilet against exterior wall /door wall and flip how door opens, of course if there is enough room either side of toilet, or a pocket door..

Now noticing where height of ceiling is, probably not feasible

Make the vanity bigger and change it to a shower other than that nothing is wrong with the layout.

But keep in mind, this is a guest bath. Not a place I'd want to dump a bunch of money.

Not sure how feasible to move toilet where vanity is, back of the toilet against exterior wall /door wall and flip how door opens, of course if there is enough room either side of toilet, or a pocket door..

You'd gain nothing by flipping the toilet and vanity, and moving a toilet is real money.