I'm going to book meeting rooms meant for studying in even though I'm usually alone
Why do you want to book meeting rooms if you are studying alone?
I want to make sure all rooms are free for me.
It can be seen as inconsiderate to take up more space than you actually need. If someone has an actual event or meeting, they will need this space to fit everyone.
I can do whatever I want. I suffer from adult ADD so I need to multitask.
Taking more space than is necessary will make you appear inconsiderate. It's important to remember that it's fine to do the things that you want in life as long as other people are not negatively impacted by your actions.