Vastu is mostly just like a human body, to construct a house 5 elements required which are 5 elements of life in this Universe. These 5 elements are : Earth, Sky, Water, Fire & Air. First Vastu Shastra was Introduced by Lord Vishwakarma, who is god of tools, Machines & Construction. Lord Vishwakarma built Dwarka also.
Vastu Purush is the appearance from the sweat of Lord Shiva, just after appearing he had a big body & asked Lord Brahma as he built all the world but did not have any place for him on earth, Lord Brahma asked to take place on all new construction with all 45 other gods.