Don't know ideal but can tell you elevated at least 6 inches off floor in a clean dry place not subject to hi humidity. A/C on all day off at night is not good for it as it causes condensation even in flour. Here in Florida on a hot rainy day when flour is delivered a 100 lb. bag will weigh about 103-105 depending on humidity even in plastic lined bags. Hard for a pastry chef here.
white flour will do fine at room temperature and not really start losing its nutritional value for several months. I keep my whole wheat flour in the walk-in as it is much higher in oil content and I don't use it fast enough that I don't worry about that oil going rancid.
where the flour is kept is a very important thing because the flour absorbs humidity and heat also. these temperature matters in your recipes and can alter results. keep it in a clean, aerated and away from heat (room temperature is perfect).