The roof will necessarily be flat and slope from the north to south. At it's lowest point it is 3m to the eaves. Is this too low? Do you think 4m should be the minimum roof height?
Does that mean it's a mono-pitch roof across the 15m? That's no problem, in fact probably an advantage for access from the north, but it's quite unusual.
3m would probably suit more livestock area tractors, but they keep getting taller and I can't get through a couple of low eaves of sheds built in the '60s. Most arable tractors seem over 10' high now, and those flashing beacons we all have to fit add another foot! The south side will obviously be the lowest for your benefit, and usually the favoured way in for ours, giving a drier, sunnier entrance apron.
I'll DM you my details.