To tell my manager I won’t share a room with colleague again?

The issue is not the colleague, it's sharing a room. It's not appropriate, unless you're in Planes, Trains and Automobiles.

You could always say that you have recently started experiencing sleep issues so sharing a room really impacts these days.

In the long run, the company will not benefit if you are too exhausted to be truly productive.

Hugely inappropriate and unreasonable of your employer to expect you to share. Just state calmly that you cannot continue with it.

This is not your concern. I've never worked for a company that expected colleagues to share a room while on a business trip. Conversely, during company "away weekends" to places like Spain or the US, the junior ranks did indeed share but going there was a perk, not a job requirement.

But her size causes the snoring. It does with my husband and the times he's lost a bit of weight, the snoring stops. I often have to sleep in another room if I have to be well rested the next day. Same with the bathroom visits, it's a good job we have two!

I travel for work and would never expect to share a room with a colleague, I think you need to push back heavily on this. I know you have gone along with it previously but its really not appropriate.

I would have refused point blank to share a room with a work colleague!

Highly inappropriate. Refuse to ever do this again.

Why should OP go to all that trouble? And it's not the co-worker's fault either - nor should she be expected to change her behaviour. Neither of them should be forced to share with anyone else.

YANBU obviously.

The only person I ever share a room with is DP, and I would refuse to do so with a colleague under any circumstances.

No way would I share with anyone even if they were as wonderful as your first colleague. If my work want me to stay away then they will have to pay for me to have my own room or I’m not going.

No way would I share with anyone friend or not. I am a terrible snorer too, my mum took me the dr over it when I was a baby. Large or not it doesn’t change anything in my case and I dont think its fair to shame this lady over it.

No way would I share ever. They want you to travel? You should get a room. You're a grown up.

But, it could be a 'reason' why not wanting to share in future as it wouldn't have come up if they were in separate rooms and can say that there was pressure to agree since they were in the room and you had to sleep in there and didn't want to cause a rift/awkward situation and that if you'd had your own room you would have been able to walk away and leave it. Instead you had difficulty to be assertive under the circumstances and it made you realise that these sort of arrangements are just not professional and you don't want to be in similar situations again.

YANBU

There’s no fucking way I’d share a room. Tight fuckers. Their financial situation is not your problem.

Oh no. I couldn’t do it

I just wouldn’t go if I had to share. The only person I share a room with is DH.

You are absolutely not being unreasonable. This isn't a fun girl's outing. This is a work trip. And if you can't get a good night's sleep and are bothered by the behaviors of your "roommate", that's going to interrupt your workflow.

It was absolutely unprofessional of her to ask for your meal allowance and even more unprofessional of her to eat in the room and not just use it for a soft drink.
She lied to you.
Does corporate allow you to give your dinner allowance does somebody else? Will you get in trouble for this?

Meanwhile talk to your coworker. Tell her you were uncomfortable with letting her buy a soda, and she took advantage of you and lied to you.
It kind of sounds like she doesn't have much self reflection or awareness of her own behavior.
Tell her that the snoring affected your work, the entire situation didnt work for you.
See if she's open to changing or adjusting her behaviors accordingly. If not, tell her youre going to approach hr and
ask for different accomodations because this rooming situation didn't work for you.
There's absolutely nothing wrong with approaching her either.
Meamwhile do a little research on cheaper hotels or airbnbs or things that would save them money but would allow you to have your own accommodations.

At least they told you at interview so you could refuse. I wonder how long it took until they got someone to accept those terms?

Is it particular industries that this happens? I maybe understand it a bit more if it is in not-for-profit/charity sector.

I have had to share when I was younger for a previous employer. I would never agree to it now as think if they can't afford to accommodate you properly, they then shouldn't be expecting you to travel.

I refused a job that included travel as they wouldn't guarantee I'd have a private room. They put colleagues in shared rooms who didn't even know each other to save money - nope, nope, nope.

I am assuming the latter!

Do you mean it's illegal to share a hotel room with a colleague or for work to basically imply it's share or leave?

There’s some good advice on this thread. I feel the OP was initially viewing her colleague as being the unreasonable one.

I hope this has reframed it as it being her employer who has disrespected them. It’s quite a demeaning position to be put in. What if a hotel ran out of twin beds? What if your counterpart was the opposite sex? Where would the line be drawn if it hasnt been drawn at the obvious privacy-respecting boundary of separate rooms for each employee?

I would just tell your work that you are no longer happy to share with any colleague. It was never appropriate to start with.

I think I would say, I was willing to share for a short period of time, but have come to realise that this is not an appropriate policy and so will not be travelling in future if expected to share.