This is an interesting stretch of Ravenswood. Many of the industrial buildings have been converted into loft spaces, yoga studios, art centers, etc. Chicago has lost quite a bit of its industry in this way, at least in the more popular neighborhoods.
Anyway, I would see this strange quarter round greenhouse-like structure from the train and wonder what the heck it was. Only recently did I discover that it's now part of the Ravenswood Event Center. Need a dramatic wedding locale for 200 of your closest friends? This would be pretty cool. It also has a narrow outdoor area with a trellis, which extends for a good 30 feet (you can see part of it to the right of the roof).
Originally this building was owned by a printing company, and they used this space to make huge billboards, which were created by painters and artists who needed the 45' high ceiling and natural light. With the improvement of printing technology it became obsolete. According to the website all of the window frames are original.