English can be tricky, but a Roadster has only a soft top. If your car has a fold down rear bench seat, it is a Coupe like mine. Mercedes sold the Roadsters with removable hardtops as Roadster/Coupes.
If your car is a true Coupe, it is not economically practical to convert it to a roadster. It would involve cutting the sotftop tub out of a Roadster and cutting the Coupe body to accept it. Then welding the tub into place and doing all of the finishing work.
There are some folks in Germany who have added a soft top to the outside of the Coupe, but it still involves cutting and welding and it doesn't fold down into a tub with a cover like the true Roadsters. The car still looks good with the Pagoda hardtop that gives the car it's nickname. I am quite happy with mine, and here in Florida, there are plenty of days to go out and about topless. In fact, I'm going to go do that right now.
Ray
'68 280SL 4-spd Coupe