You cannot sue the builder for this because it was not a "latent" or hidden defect which you could not know of unless the builder specifically disclosed it to you: based on what you write, it is a large ditch in your front yard. Therefore, you knew--or had the easy opportunity to know (such as by visting the property before putting in an offer) of it before buying the property; having bought the property with an obvious condition, you give up any claims against the builder for that condition. Your purchasing it with awareness of the condition waives your right to sue.If they put an agreement to fix the issue into writing *before* you closed, you could, however, enforce that agreement--but it would have to be in writing, and have been made prior to closing, since after closing, when they have already been paid, you are not giving them any more "consideration" for the agreement, and so it is not binding.As to whether you may legally fix it: that depends on local zoning laws and whether there are any restrictive covenants in your deed or rules/regulation in your community (e.g. if there is an HOA) preventing it. If there are no local or community or deed restrictions, you should be able pipe it.