Nobody's perfect, developers included. It is not uncommon for reputable developers to offer to repair certain construction deficiencies. While this is generally a positive circumstance, a certain degree of caution is warranted. The reality is that you are thereby expecting a company which performed the work inadequately the first time (and perhaps on numerous subsequent occasions) to suddenly do the work properly. Thus, even where the developer has agreed to make repairs, it may still be wise to retain a competent lawyer and/or expert consultant to evaluate and monitor the developer's proposed investigation and repair.