There are two interesting articles in the Financial Times today:
According to the first article,
The revision, equivalent to adding a country as big as Belgium to the estimated size of the world economy, will make the US one of the first adopters of a new international standard for GDP accounting.
which links to the 2008 SNA page.
The manual/handbook of the new SNA is available at the Unstats site.
It is also available in print for $150 or $75 (depending on where you live).
It is the book to learn national accounts and is better if read from the start rather than being used as a reference for one particular point. When you read it patiently, you will realize how much of work and effort has gone into it – especially to make the conceptual framework self-consistent.