Templates that are engineered to contain a predetermined sequence and a hairpin structure are provided by a nested oligonucleotide extension reaction. The engineered template allows Single Primer Amplification (SPA) to amplify a target sequence within the engineered template. In particularly useful embodiments, the target sequences from the engineered templates are cloned into expression vehicles to provide a library of polypeptides or proteins, such as, for example, an antibody library.