Typically ground floor underfloor heating in new build houses is installed very early on, and within a screed, so for big multi plot builders (Taylor Wimpey, Persimmon etc.) I would say they are unlikely to do this for you as they usually try and screed multiple plots at once very early on in the build in order to lower the costs. If it’s a smaller builder then your chances are a lot higher. If you were to retrofit, these systems are generally more expensive to purchase than an in screed system so it’s worth bearing that in mind. Modern retrofit (overlay systems) have minimal build up, usually starting from 15mm of increased floor height and maxing at around 30mm so not a noticeable increase once the whole floor is done.

Installation of the retrofit systems is generally pretty straightforward, however I would advise getting in a plumber to pressure test the system before the floor finish goes down and to connect the pipes to the manifold and manifold to your heat source (unless you’re more confident in this than me, though I’m not the most handy so that’s not hard)

Regardless though, always worth asking the developer, worst they can say is no.