There are a couple of specifications you’ll need to pay attention to. If you are mounting a base bar system to a slick roof vehicle then the towers have a max load rating. There are also the crossbars that may have their own max weight. Then, finally, if you have base bars installed from the factory those will have a maximum weight also. Follow all the specifications and the only thing you’ll need to worry about is dropping the bike on your roof. It does happen but if it does, the worst is probably going to be some paint scratches. Generally speaking, you have to lift a bike above your head to get onto a rooftop bike rack so that is going to rule out heavy electric bikes anyway.