For the construction of the foundation, many factors are considered. Type of soil, slopes, drainage of subgrade, structural loads etc.
For the construction on steep slopes, make a structural drawing from a localised structural engineer. that person gives you a better idea for. Constructing a foundation for your land by analysing the type of soil and water table level. The civil engineer also takes care of all the local government regulations.
As you ask in a question, the architect only designs the outer surface and interior of a building, but not the structural design, foundation plan or construction plan.