To better budget your limited amount of total hobby time, maximize your railroading time by minimizing your modeling time [ESSAY].
Papercraft is the oldest form of railroad model structure crafting. Paper is cheaper than wood or brass, it does not require painting like plastic, and thanks to modern color printers it can display a level of illustration detail once only available on lithographed tin. Port scenes are especially suitable for Papercraft, as you can inexpensively build full O-scale merchant ships and waterfront facilities (see page 61 in the book "Waterfront Terminals and Operations"). Regular paper will absorb humidity though, so to prevent book mold or sagging, use one of the modern heavier-weight treated papers (or better yet, cut and paste the paper onto styrofoam).
There are a few O-scale pre-assembled plastic structures available, but they typically will be undersized in regards to the footprint required by the business indicated. Although these pre-assembled structures are the quick solution to decorating your layout, the better solution is usually to custom construct (including when building from a kit) your own structures, so they will fit your layout vision exactly. Scratch building is best done from scale plans, but you can get your measurements from a photograph, as long as you correct for perspective [EXPLANATION]. Unless you are building a diorama for a photo shoot, a structures handling durability should always trump fine detail fragility.
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