Vikings are often depicted as being exceptionally tall and well built for their time. I know that they kept no written records of themselves and every written account we have of them is written by the people who they invaded, so they may have depicted them this way deliberately. Their diet seemed to be more protein and fat rich compared to most of the people they invaded and they seemed to live quite active lifestyles. These days as well most northern Europeans are tall and well built. How true is the depiction of vikings being exceedingly tall and well built for their time.
Hi there! The thing to keep in mind about your question is that, properly used, the term "Viking" refers to an occupation, not an ethnic group or proto-nation or whatever. That is, "vikings" were people who participated in viking activity: seafaring raiding, banditry and piracy along the coasts and even far inland in Europe during the "viking age." The term in English has been used more loosely to denote the group of people who produced viking raiders, that is the Norse population of Scandinavia, since the mid-18th century, gaining popularity in connection with the various Scandinavian nationalist movements of the 19th century. So asking how "Vikings" were built is a bit like asking how, for example US Marines are built -- they are people who self-selected for a military or militaristic lifestyle.
That said, as you await more answers, some of these older questions/answers might be relevant to you.