I've spent 35+ years in mortgage lending, specializing in builder business. It's not unusual for a builder to ask for the entire downpayment upfront, if the downpayment is only the minimum required for the loan program (FHA, VA, Conventional, etc). When a buyer is making a larger downpayment, say 20-30% or more, the builder will ask for the DP to paid in "progress payments"; i.e. installments that coincide with construction phases of the house.

The idea is obviously to keep the sale together. Buyers are more likely to back out of a contract if they have nothing at risk. I know builders who have started construction of $500,000 houses with only a $1,000 deposit. That's totally insane. These are the guys who find themselves up to their necks with inventory....who are sucked dry by construction loan interest....all because they were stupid enough to move dirt and start spending money without a committed buyer on the other side.

You've not raised a single issue, aside from the fact that you want to be able to walk away from a legally binding contract if you choose to do so. If you have concerns about job loss, you have no business buying a house.

If you were my customer I'd tell you to take a hike.