Do chickens need grass?

[Eyren]

We are currently building our hen hotel and are having paving at the bottom of the run covered with woodchips or something like it. We're also putting a corrugated plastic roof on-will this be enough to keep them happy? Planning to get 3 on saturday

That should be fine - add something to perch on, such as a narrow but sturdy log, and give them some greens to peck at, and that's all they really need (apart from the obvious - food, water and mixed grit).