Update: The massive survey of historic buildings adopted by the city in 1994 tentatively identifies this building as a work of Titus de Bobula. That would certainly explain its eccentric style: Pittsburgh never had another architect like him. It would also date the building between 1903 and 1910. If we read the map correctly, it first appears on the map layer dated 1903–1906 at the Pittsburgh Historic Maps site, so this might have been one of de Bobula’s early commissions here. Our original remarks appear below.
It has not been possible to find any information about the age or architect of this curious building in the limited time old Pa Pitt was willing to devote to the task. The researchers who compiled information for the Firstside Historic District also threw up their hands. It is a mostly utilitarian small warehouse, but with angular decorations that suggest a prickly version of Art Deco. Right now you can buy it if you like, and then you might find more clues to its origin among the debris of the decades.