use an Architect - get the design you want, and specification sorted before approaching any builders. In this way you:
- develop the design you want using a professional team, exploring layout options in detail. with any extension it is important to get the whole house balance/accommodation right to maximise value.
- develop structural designs to work best with layout
- understand party wall matters and approach correctly, this can be a major cause of disruption (ie cost and delay)
- get a good understanding of costs through design process
- go to a number of builders with a defined set of drawings/scope and get good comparison costs
- pick the builder that works best for you in terms of quality, cost and time.
- get the right contract
- understand your rights as the building owner and get the right contract.
following this process puts you in control, and mitigates problems on site, and therefore cost escalation. using an architect saves you cost and time - and improves quality.
good luck!

I'm interested in this too so just marking my place

Hi,

A friend of mine used these guys and was very happy with the results.

http://www.lifestylebyasq.co.uk/

Or there's a few here worth looking at:

http://www.theartofbespoke.com/sourcebo ... and-build/

Good luck

Hello - I am 10 months into a year long project with PASK (http://www.pasklondon.co.uk/ who are a design and build company run by two brothers. We have had a complete rennovation including basement, kitchen extension (we have had a separate architect though). All going well so far and would be happy to provide furthe details if you wanted to send me a PM (I would add though that no project is without a certain amount of stress particularly when you get to the stage that we are at when major decisions need to be finalised every day).

Hi

I've just moved and am now looking for someone to do a kitchen extension, attic conversion, some rewiring and replumbing, replace bathrooms and a few other things.

Ideally, I'm looking for a one stop shop who could deal with both the design and the building work.

Can anyone recommend someone reliable?

Thanks