“roof box” is correct and usable in written English.
You can use it to refer to a box, usually made out of metal, that is attached to the roof of a vehicle in order to carry luggage. For example, "We decided to purchase a roof box to store our camping gear in for our road trip."
I've bought a roof box for the family car.
Our roof box – the Thule Atlantis – is the only thing we own that takes its name from not one, but two, mythical kingdoms.
Labied Razzaq, retired from running a software business, has driven from Northampton with 105 pairs of shoes in a roof box, and is giving them to people wearing flimsy flip-flops.
Many, like ours, were equipped with a five-year-old and a baby too, along with a roof box in which to transport the necessaries of holidaying with the very young: tranquilliser gun and darts, immobilising net, earplugs and medicinal brandy.
Above the entrance to the Newgrange tomb, which takes the form of a large grass-covered mound, is a small "roof box" that is aligned to the rising sun, a piece of design believed to have functioned in the past as an indicator of the new year.
The pièce de résistance is a clear-coat carbon roof box.
The ExCel Center supplied an astonishing smorgasbord of sports under one roof: boxing, fencing, judo, wrestling, table tennis, weight lifting, taekwondo.
"Man, that hawk is hitting this guy's bird!" Tyson sprang out of his chair and hobbled across the roof — boxing was not good to his body — bobbing between satellite dishes and piles of two-by-fours.
On top of the open roof, a box was installed with openings for spotlights and a camera.
I sprang for the $1,500 or so to buy the whole lash-up antenna on the roof, three boxes for our three TVs–and a tech came down and hooked it alash-up antenna
The attic in the 1850s part of the house is not finished, and the gable roof has "boxed cornices with returns".
