The Windsor Park by Gwathmey-Siegel condominium building at 100 West 58th Street is about 70 percent sold.

The 14-story building was formerly the Helmsley Windsor Hotel, which had 242 hotel rooms. It is being converted to 103 condominium apartments by Yitzchak Tessler and Meyer Chetrit, who commissioned Gwathmey-Siegel to design the interiors and a roof-top addition.

The brown-brick, pre-war building is on the southwest corner of the Avenue of the Americas and is just to the north of the Jekyll & Hyde Club. The conversion involved the creation of duplex units with double-height living rooms at the corner and a large barrel-vaulted penthouse structure.

According to press reports, the two penthouses are still available for $13 million and $16.25 million and Angela Lansbury, the actress, recently bought an apartment in the building for about $2 million.

Sale closings began last month.

Some of the apartments in this project along the avenue will have partial views of Central Park, which is one block to the north.

One of the penthouses has 3,917 square feet of interior space and 4,028 square feet of exterior space with a wrap-around terrace, four bedrooms, five baths and two fireplaces. The other has 3,414 square feet of interior space and 231 square feet of exterior space with four bedrooms and five baths and a living room with a 25-foot-high, vaulted ceiling with circular, bubble skylights.

Gwathmey Siegel is the architectural firm that designed the sinuously curved apartment tower at 26 Cooper Square as well as many academic and institutional buildings and residences. It was one of the "New York Five" or "Whites" architectural firms that emerged in the 1960s and were known for their Modernistic white buildings.