Usually you have a pretty high rate construction or bridge loan that you plan on refinancing into a normal home loan when there’s a house to backstop it.
But you can’t get that backstopped loan until the house exists.
Likely you could pull out and lose a deposit (and a good lawyer might even get that back because of delay) but you’re still without a house.
The builder we used builds to spec and then you buy the house minus the initial deposit in full. He’s not a fan of doing customer-originated/owned construction loans, which is fair, I believe a good number of builders in our area operate the same way.
But you can’t get that backstopped loan until the house exists.
Likely you could pull out and lose a deposit (and a good lawyer might even get that back because of delay) but you’re still without a house.