I don't recall that (that he owned the place) but I do remember he is generally portrayed as a bit of a miser, though he usually goes along with the crazy scheme of the day.
Fred Mertz has his own Wikipedia entry (lol), which states:
"Eventually, Fred and Ethel retired and bought a brownstone apartment in New York City. In 1942, Lucy and Ricky moved into the brownstone apartment building where Fred, Ethel, Lucy, and Ricky quickly became friends. Fred's best friend, Ricky Ricardo, and Ricky's wife, Lucy, live in the apartment house."
Here the link:
Fred