whats the difference between buildings and pyramids?

Answer 1

Pyramids start with a large base then end with a point, buildings (traditional buildings that is) are just an elongated box.

Answer 2

There are many types of buildings: houses, factories, apartments, warehouses, shops, pyramids ...

Pyramids are just one type of building. They have a particular shape so that all sides apart from the base (and maybe even the base) are triangles, so that there is a point on top.

If you look around, you may even notice that the roof of many non-pyramid buildings is shaped as a pyramid (houses, some skyscrapers etc) and, no, I don't think this is all part of some conspiracy out of the DeVinci code.