Range from the cheapest single storey extension £50,200 (Astraway Construction Ltd. based in SW16) to the dearest single storey extension £95,000 (Felix Building based in SW16).
Comparing extension builders estimates for fitting a downstairs toilet gives you an idea of who will be better value but the best way to compare costs is to get actual quotes.
What to do - Get rates and quotes to build a single storey extension in SW16 by posting a job with HaMuch and we will send it to extension builders in SW16.

"Single storey extension"
BALHAM