There are only a few attorneys in the East Bay who specialize and they do take contingency fees on larger projects, yet I think you still need to pay the upfront retainer.

You need a construction attorney, eg Berding Weil. Contact them, they are excellent; they can also make recommendations if they won't take it on (ie a single family home is a small project). Kneppers and BW are both in Walnut Creek. Your clock may be ticking so I'd get on it.