One of Milwaukee's largest apartment building owners just added hundreds of new apartment units to its portfolio. : One of Milwaukee's largest apartment building owners has added hundreds of apartment units to its portfolio. On Tuesday, Katz Properties bought up a slate of apartments and commercial property from Blankstein Enterprises, another local apartment building owner. The sale included 11 buildings — and a total of 784 units — according to investment firm CBRE, which facilitated the sale. Blankstein Enterprises has been selling off many of its properties recently.