Having turned one of our rooms into a study for my wife, the box room is mine. You might suggest that it is a little extravagant to have a study each, but my wife's study is a very personal space for her, and whilst she lets me use it to work from home, she does so grudgingly ;-)
For the last couple of years my wife and I have introduced a tradition of making our gifts for each other. This year that gift was what I am calling a 'lap desk' but I guess it just a freestanding mini desk that has a tilting top.
In our house, one thing was made very clear from before we even moved in. The garage is my territory, and the study is my wife's.