A Shack?
Ignaz von Seyfried (1776–1841) was the musical director of the theater from 1798 to 1801, continuing in this role at the Theater an der Wien until 1826. In 1840, he wrote a contribution to the Neue Zeitschrift für Musik (12/46, 5 June 1840) in which he described the Theater an der Wieden in rather derogatory terms: "... for that limited venue, not much better than a wooden shack, Mozart composed his immortal Magic Flute". As recent archival research has shown, this description is certainly false.
Read more about this topic: Theater Auf Der Wieden