I put my hardtop on my Z4M every winter. It's really a 10min, 2 person job that's really easy. IMO the look of a roadster with a hardtop is ok... It's not the same as the beautiful coupe, but it's ok.
Here is mine with the hardtop on...
Z4M roadster vs Z4M coupe. It's common knowledge that the Z4M Coupe looks better then the Roadster and that the Coupe is more exclusive then the roadster... I own a Roadster and IMO the Coupe does look better, but when driving with the top down the Roadster is more fun for me. If I bought a Z4M coupe then I had a small unpractical sports car, if I bought the roadster then I also had a small unpractical sports car but with extra added value of also having a convertible. If you don't like driving a convertible or are so in love with the looks of the coupé. Buy one! It's that easy!