I don't think it's roof or windscreen, it's both if you want to stay dry. That's a big increase in size, mass, and wind resistance (including susceptibility to side winds that can tip you over). That might have you consider having more than two wheels for stability, and windshield wipers, and a big battery to haul all that... at some point, we'll be wondering whether it's a car with pedals or a bike?
You can build electric cars that are traditional two ton vehicles or you could build electric "cars" that weigh 95% less but still protect you from the elements. Like the PodRide https://www.youtube.com/watch?v=F4xgpOBrEp4
https://www.daimler.com/company/tradition/company-history/18...