Both Roman Empire and Han dynasty had to defend their northern boarders against powerful enemies, so both of them had the motivation to build a great wall along their northern boarders.
Roman Empire and Han dynasty had roughly the same size and population. If the Chinese had enough resources and manpower to build a great wall, then the Romans should also have.
Why didn't Roman Empire build a great wall, as the Qin dynasty and Han dynasty did? Did it not make sense for them?