Anyway, I came across a listing for 203 E. 13th St. #PH4B. Apparently this one has been on the market for some time. This PH doesn't include the cabin, though you at least have use of part of that rooftoop space...
According to that listing:
Own a very unique penthouse apartment in the Historical Kiehl's Building built in 1851. This astonishing loft like large one bedroom is in pristine condition with soaring 11 ft ceilings and is flooded with sun. This stunning apartment has original exposed brick & enormous brick arched windows all facing south. It comes equipped with a washer/dryer, built in security system and a beautifully renovated kitchen and bath. The spiral staircase leads to your own very private roof garden oasis of over 400 sq ft! Pets are welcome. Come and see for yourself. Own a piece of history in this boutique condo Penthouse of the historic Kiehl's Building now called Pear Tree Place named after the pear tree that once grew just beyond the front door.
This space can be yours for $1.265 million (715 square feet). But that price doesn't include the hellacious views that you'll have of the mystery lot next door!