I use aluminum rail, code 332 which I purchase from California & Oregon Coast Railway (http://www.cocry.com/)...though I believe that is a micro engineering product. If this is a storage/fiddle yard, I'd encourage you to be creative as even aluminum rail will be an expense for any considerable size. In my train storage cabinets I went from sectional track cut to fit to aluminum rail spiked to the shelves to wooden rails made from quarter round molding to two grooves cut into the shelves. For any additional storage I construct, I will be using the method that Ray Heckman devised in the Feb. 2008 Garden Railways (page 52) where rather than rails, a flat (1/8" - 1/4" thick) strip of wood or other material who's width is slightly less than the back to back wheel spacing (1 5/8" is cited) is used to guide the cars. For a drive in storage yard, I can conceive that you could transition from "regular" track to wooden rails that tapered down to the shelf/substrate guiding the cars onto such a storage mechanism.