Sorry this is happening. I assume you've already complained to the builder and they have not fixed it?

Next thing is to find out who is in charge of building permits and stormwater control for construction sites. Are you in a city or out in the county? If in an incorporated city I would look first for the city building permits office. If out in the county, depending on the county, there will be more or less of a building permit office. I happen to live in MO so I know. :-P

It is generally frowned upon and/or illegal for sediment to be leaving a construction site either into streets, waterways or neighboring yards. That's a 'land disturbance permit' issue that applies while the construction is going on. If you're in a city, there should be requirements for silt fences or other structures to prevent it, and a stormwater pollution prevention plan.

After it's done, the design itself should not be dumping water on you either, so you might want to make sure the design was approved as part of the building permit. Otherwise your problems may not end when the construction is done.

Contact your building inspector or the local EPA office. These days, many municipalities have requirements to protect the environment from run off of mud from construction sites. Around here, before anyone can break ground, a crew installs plastic erosion barriers around the site, the bottom edge of which is buried in the ground. This was enacted to protect streams, but it also protects adjoining properties. The EPA may have more clout than the local authorities.