I have had some success with erosion control by making SHALLOW ditches across the slope so it redirects the water on a better path down the slope. This slows the water flow and prevents erosion. These "ditches" only need to be an inch or so deep and a couple of feet apart, nothing that will effect the lawn when the grass is grown.

The idea is to get the water off of the slope so there will never be a rushing mini torrent in any one place.

If there is a large flow down the slope that will have to be handled first, and then the minor water flows can be handled with the ditches described above.

Do not till. It will take a few years for the ground to settle afterward leaving uneven areas. Just scrape the area (box blade is great) level and seed or sod.

DO NOT TILL, just to follow up and agree with neliaz. If the contractors left your soil surface uneven, then the box blade is the universal solution.

If you sod, you can do that any time from now on. If you decide to go with seed, wait until mid June. Bermuda seed needs hot soil (not hot air) to germinate. That would give you many more months to worry about erosion. Until then you can just mow the weeds and practice taking care of it like it was Buckingham Palace.

Seeded bermuda and sodded bermuda are two different varieties of plant. They do not mix well in a yard, so think about that before you go buy any seed. Never seed bermuda to patch up a thin spot of hybrid (sod) bermuda.