It depends on what your winter temp extremes are, how deep the frost line is and how high the water table. Like Poltax said, root storage can be as simple as storing your crops in a buried fridge/freezer--IF your water table is not too high and your frost line is low enough. Here in ND, I'd have to bury the fridge at least 3 ft, 4 to be safe. But the water table is about 2-3 ft, so that wouldn't work for me.

That's for a root cellar. But if you have a cool basement (like mine) that would work too. The idea is to be cool (around 35°-45°) and relatively dry. You do NOT want it to freeze, so usually a garage won't work unless it's attached and you can control the heat.