I'm spending much of the day in Portcullis House - the most recently built part of the Parliamentary Estate. It is a fine building - which led to some controversy, as its costs, originally estimated at £165m in 1992 - turned out to be £235m. A report into the cost overruns was never published. When she opened it, the Queen commented that "the building complemented and contrasted with the Palace of Westminster" - a judgement that I would agree with.
Portcullis House has a number of offices for MPs as well as a series of rooms used for committee meetings. These are a vast improvement on the cramped offices and acoustically challenged committee rooms in the Palace itself (though a cramped room in the Palace is more sought after by MPs - on the same grounds that the nearer an office is to the Oval Office in the West Wing, the more prestigious it is - howver small it may be)
The parliamentary website has a series of pages on the history; architecture and energy saving characteristics of Portcullis House, which is accessible here.