You mean a round bed? I get that technically it would be a cylinder but people also don’t commonly refer to a normal rectangular bed as a cuboid bed :)
I have a triangular bed (I live in a boat) and you end up with a few unused spots. I think a cylindrical bed would be even worse in terms of "dead space".
I have a friend who had a cylindrical bed in college (and maybe still now). It's fun but takes up more functional space in the room for less usable space on the bed. Also much harder to build and get sheets for.
