罗马不是一天建成的，但是你可以一天就把他毁掉

Rome was not built in one day, but you can destroy it in one day.

个人意见,或者看看其他朋友的意见吧.呵呵

Rome was not built in one day, but you can hear one day he destroyed

Rome was not built in one day, but you can destroy it within one day.

Roma was not bulit in a day ，but it can be destroyed in one day

Rome is not built in one day, but you can destroy it in one day. 前后都用in one day，会有点排比得感觉。