The Cachet Boutique hotel and its elegant Playboy Supper Club at 510 W. 42nd St. are being topped with a private rooftop observation deck and performance space fronted by a huge LED billboard.

Known as the Glass Cube, it is being created for the private use of brands that lease the billboard for launch events such as music tours and products.

The hotel owners and developers are Merchants Hospitality, led by Abraham Merchant, Richard Cohn and Adam Hochfelder, along with investor Robert W. Roche of Roche Enterprises.

A $42 million mortgage funded by Taconic Capital Advisors and just obtained through Robert Verrone and Christopher Herron of Iron Hound Management replaces the initial construction financing.

The funds were used to renovate the 151-key hotel, Merchants’ Treadwell Park restaurant, the Sky Box and Retreat private event spaces, and the Playboy Club and its Black Box event space.