Before you read any further, do me a favor and examine the close up pictures of the Market Street warehouses. Those photos are from 1906, so they're a good twenty-five years before the era I model. When you look at them, how worn, dirty, or unmaintained do you expect them to be? How much is your opinion based on photos from the same era, and how much is based on similar buildings you've seen recently?
One of my big challenges modeling an era that I didn't live through is that I don't have a good idea of appropriate weathering for the various buildings. I remember some of the old warehouses and buildings along the railroad right-of-ways from my childhood in the 1970's, but the condition of SP's warehouses under what's now Pac Bell (er... AT&T) Park probably doesn't hint at what they were like in the 1950's, or in the 1930's. Photos help a bit, but my own biases mean I'll aim my industrial buildings too worn if I'm not careful.
With the Market Street warehouse, I'm doubly cursed - the buildings I'm modeling on appeared some time between 1915 and 1935, but other warehouses and packing sheds in the area probably date to the turn of the century, or perhaps even to when the San Francisco and San Jose Railroad first visited San Jose in the 1860's.
On top of just deciding on age and era, most of the packing sheds and other buildings used for part of the year don't appear to be well maintained even in good times, as can be seen from these photos of contemporary packing houses in Central California.
I decided to model my warehouse with moderate to severe weathering, trying to capture the look of paint that's wearing away and wood that's darkening. I tried a technique I've used before to model weathered, bleached wood: distress the styrene, cover with primer or gesso, then use india ink and brown washes to bring out the texture. Here's a photo of the warehouse so far with the walls painted, but no roof or view block to keep the sky behind the building from poking out - it's not perfect, but it'll do for now.
So how do you determine how worn your buildings should be?