Builder asking for proof of funds

[Summer2019NewMummy]

Hi

I'm getting a builder to build a house for me, that I've got planning permission for.

Is it standard for him to ask for proof of funds?

What deposit is reasonable for him to expect upfront?

Not unreasonable. However get a clear contract including payt schedules and options to withhold in the event of lack of progress. No deposit and ensure at least 20% terminal payment withheld for a month after completion of the building control cert to ensure you are happy and all snagging done. Decent builders expect that. Do not pay anything up front