Signed with first choice builder (glowing references, reasonably good quality of viewed builds & good to get on with), on terms not far off what we aimed for. Many thanks to all on the forum who helped us edge forward to this stage. Perhaps the experience so far can help others who are at an even earlier stage with even less experience than us.

Financial terms in essence are 50:50 pain or gain share with builder, after protecting their normal profit & overheads + allowing them builder contingency. The lower the hard costs (paid to suppliers) the more the builder makes (and we save). Price increases during the build to be borne 50:50. Variations to be priced benchmarked against SPONS, and if too pricey (or even if not) then we have the right to seek alternative quotes (potentially needing to pay 10% of quote as builder's profit/attendance). If supplier credit unavailable for some items then they will request payment when materials arrive on site and are vested in us, but we retain the right to grant that request or not.

We started off telling them that we were interested in a target price without too much "just in case" pricing, with fair profit/overheads that preferably did not depend on marking up costs. Instead, they would get a share in cost savings. Then we sent them (and some other good builders) detailed drawings & specifications plus Estimators Online, something like a bill of quantities & programme of works. They then got their own Estimators Online quote, marked it up a bit, eased the programme of works a bit, and submitted it to us in that format. Hopefully these details will make it easier to value work completed. No deposit, but weekly payment for work completed. At least two thirds of the final completed build is awarded.

 

Relief at getting to this stage, but the work of trying to find better quotes goes on.
Thanks again to all for the excellent advice and sharing of experiences.

Well done that sounds promising.

 

Decent references count for a lot.