How can I weather model railroad buildings?

A garden railroad or garden railway is a model railway system set up outdoors in a garden. Most often, it is #1 gauge rail track with a G scale or similar train. LGB first popularised these trains, and more recently other manufacturers such as Aristo Craft Trains and USA Trains have prodcued models in this scale/gauge combination. Atlas O also makes weatherproof #0 gauge tracks for O scale, very suitable for smaller gardens and patios.