The owner(s) may con­vey title to lots in the improved por­tions of the sub­di­vi­sion, pro­vid­ed that streets, storm and san­i­tary sew­ers, and sewage treat­ment plants be designed and built to serve the entire area or be ini­tial­ly devel­oped in such a man­ner that they can eas­i­ly be expand­ed or extend­ed, as the case may be to serve the entire development.