What a nightmare. Fortunately my wife is as happy watching stuff on a stupid ipad as much as a projector.
That said, when we bought our hours over 25 years ago, I always planned to build one. About 15 years ago, we did major renovations (is was a Queensland, Australia Colonial wood house, on stumps) and the common thing is to raise and build under. So we did that, and I set aside one room for my HT. Tech was pretty bad and expensive back then so it was on the backburner, and just used for storage junk. My plan was to finish the renovation of the rest of the house. So for 12 years or so of weekend and holiday work I went though fully finishing (eg stripping back to timber and repainting) the entire original 100+ year old sections, inside and out, floors etc, built HER craft room, and everything else, and finally got it finished, and by then had paid it off, and I said Ok now time for MY room, so I cleared it, started planning, designing, then building etc. I did most of it myself, except the plaster / drywall (that is beyond me).
And you note above on the renovations etc, I used the term "I", not "we". That is not an oversight.
But you know what? As soon as I got it cleared out and was planning shelving, etc, my wife asked me if I could build a cupboard at the back of the room to put her ironing board into. Ignoring the fact that she HAD a cupboard for the ironing board in her mess of a laundry/office, just full or more of her garbage. It still wasn't enough.
She didn't get her extra cupboard.
I guess the moral of the story is some people are just takers/users in relationships, and there is never enough... If one partner can't even have one room for themselves under there control, but the other partner can have MULTIPLE rooms just for their use, that is just messed up.