Penthouses are a staple of upscale urban living. Ever since the new city royalty of Industrialists and entertainers transformed the lofty dead spaces created in the thrust of upwardly mobile New York in the early 20th century, the penthouse became the place to be. From the outside, Paul McAneary Architects' Tex-Tonic House is a subtle addition to London's roofscape. Tucked behind the mansion blocks and office slabs of Westminster, this new apartment occupies the eaves of a former Post Office depot, pushed up into the roof vaults and wrapped on one side by a narrow terrace and vertical garden.

This is a generous space; there are few central London apartments that span the width of a city block, with a clear view from street to street from the living area to the south through to the kitchen in the north. McAneary, who once worked in John Pawson's office, has tackled the client's demands with gusto. The most apparent and elaborate feature is the transparent wine cellar, suspended from the ceiling vault in a corridor of glass. The client - a serious oenophile - is a major collector, but figured that rather than tuck away his future vintages in a below stairs cellar he'd prefer to keep things on display. The result is a technical tour-de-force, a climate-controlled attic space that keeps over 3,000 bottles suspended on their sides - so the labels can be seen - on a series of finely tuned metal wires. Concealed uplighting makes the bottles glow, turning the entire cellar into an installation.

Elsewhere in the apartment, McAneary and his team have used the expansive floor area to play with scale and materials. From the entrance door - a vast slab of 200-year old Rhodesian Teak that stands nearly 4 metres high, through to the wood-clad 'boxes' that conceal the bedroom suites, tucked away behind concealed doors off the main living area, everything is supersized without losing its domestic qualities. Loosely inspired by the postal depot that once sat below them, the three 'post boxes' containing the bedrooms are concealed from view, containing many hidden delights, like skylit showers and dramatic hand-cut lava stone walls in the bathrooms. The exterior walls of the boxes are formed from a combination of rough-cut oak, burnt, blackened timber and a cast-bronze cladding, a rich, dark veil of metal that will eventually start to patinate nicely.

The slender mezzanine houses the wine cellar, a study and a discrete seating area, running around the L-shaped space at the highest point of the vaulted ceiling. Original, restored, roof timbers are much in evidence and the solid character of all the materials used - from the bronze and wood down to the wood-shuttering on the concrete fireplace - gives the space its tough-sounding name, the Tex-Tonic House. Technology is also pushed to the fore, from the high-end enomatic wine dispenser in the kitchen through to the concealed B&W speakers and KNX home automation system, enabling iPad control of all the house's main functions.