We first saw Quartz's Zach Seward tweet about the cost of the roof deck.
For the entire space, which Twitter moved into just last year, it must pay roughly $7.5 million per year in rent.
Twitter is also reportedly in talks to open up an additional office adjacent to its current HQ.
The microblogging platform, which just filed its IPO last week, is likely to be valued at $20 billion or higher in its first trade.