Jim - Assuming that you are indeed in Michigan, as your screen name implies, and your layout will be situated in a normally unheated pole barn, I'm going to go against the general trend of advice offered so far.
In my opinion, the huge range in temperature and humidity in your locale potentially could create some very significant problems. First off, depending on humidity sources within and without the building, particularly during winter and springtime when going from extreme cold and dampness, to heated, then back to extreme cold, is likely to produce highly significant condensation over time. Then, too, there is the expansion/contraction cycle, particularly between differing metals/materials, that the layout tracks, solder joints and even individual parts of rollingstock will repeatedly be subjected to. Even glues and other adhesives can fail as a result of exposure to such conditions over time. Plus, cyclic changes in the layout's benchwork might be anticipated. All this in addition to the problems already cited concerning locomotive lubricants.
While, when situated in milder climates, one can get away with such essentially "outdoor" layouts without experiencing much in the way of serious difficulties, I'm really quite doubtful that this can be successfully accomplished in Michigan over any length of time without employing at least minimal measures for controlling building temperature and humidity.
NYW&B