Follow the Bermuda Bible over the winter and for the rest of your life. Google it, download it, and memorize it.

Where do you live?

When did the builder put the lawn in?

How high/low do you mow it and how often?

What is your watering schedule (frequency and duration)?

What is the preemergent you used, and how much is too much? I can't think of a reason why the preem would cause it to become brown.

Do not try to level a bermuda lawn in the spring. Either do it in the dead of winter or in the hottest heat of summer.