A BART commuter with a keen eye might notice the two unusual buildings at Castro Valley Station, tucked at the far end of a parking lot.
They have a farmhouse look, with brown utilitarian siding and black windows that reflect the overhanging trees. A white picket fence surrounds the prefab structures, which are nestled on a trailer with metal stairs that lead up to a wide deck. In better days, it was adorned with rattan mats, patio furniture and a teal beach umbrella.
The whole installation spans 16 parking spaces — asphalt that BART once advertised as prime Bay Area real estate…