I have no experience with RTTs since I dislike them.
But you will need a roofrack that will support the tent.
Also, from what I hear, a hardshell RTT is better than a soft one, I guess they last longer and easier to setup.
They cost a lot from what I can tell.
My suggestion is to shop around for RTTs and see what the features are across the board. Donut Media did a video comparing a $700(ish) to a $3500 one in their current Hi / Low comparison series. (youtube)
You aren't getting into it cheap, but features add cost. I would also pick a tent before getting a roof rack so you know you are getting one that works, or a tent may have an option to have a built in rack, etc.