Range from the cheapest single storey extension £47,000 (Cappson Construction Ltd based in BR5) to the dearest single storey extension £53,560 (EVConstructing Ltd based in DA15).
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 Sidcup by posting a job with HaMuch and we will send it to extension builders in Sidcup.

"Single storey extension"
DA15