If you don't install gutters, make sure that you have enough drainage around the building to get the water away from the building quickly, and that you have a band of gravel/rock that won't spray soil onto your nice building when it rains.
While I prefer no gutters, I try to have at least several feet of overhang to get the roof drainage out and away from the building walls and foundations, along with any necessary subsoil membranes and drainage to keep the water from soaking into the soil along the foundations. With a metal wall it is less of an issue, but I think that proper drainage away from the building is still vital.
All the best,
Peter