As "Vikings," the Normans were good SHIP builders. Once they reached land, it wasn't much of a stretch for them to transfer their skills to building churches and other buildings.
The Normans adopted a style of architecture that is known as "Romanesque." It was originated by the Romans, but later imitated by many west Europeans, chief among them the Normans. This style made use of rounded arches and was milder than the "Gothic" style, with pointed arches, that had been brought to Europe by the Goths and Visigoths at the beginning of the Dark Ages. As to why the Normans were such good imitators,
The Normans were described by others (in modern terms) as hungry, ambitious people.
Hence, they showed a greater desire to learn (and imitate) than their European peers. It appears to have been part of the restless "personality" that caused them to leave Scandinavia in search of more hospitable climates. Once they found them, they became "more royalist than the king," that is more "European" than the other western Europeans.