use a consumer protection guarantee , this guarantee protects you and your home from cowboy builders.You only pay each stage of the build when you are completely satisfied. In the unlikely event of a dispute , a chartered surveyor is dispatched to the job to adjudicate, there and then! A contract is written up in plain English. No deposits are payable up front , the first stage payment can me arranged so that it is paid when the materials are delivered to site and the work has started , protecting you from runaway rogue traders
There are many online services that state that they have quality tradesmen, but take care to research what support they give you in the event that something goes wrong! In a few cases they offer arbitration (a chat) then it is off to court - and nobody needs that level of stress!
The Consumer Protection Guarantee web address is : www.tcpg.co.uk - it cost nothing to check it out -