Why is a building called a building if it's already been built?

It is called a Building: Because the suffix 'ing' is added to verbs to make noun forms. For instance a celebrity's following. Following describes the people who follow them in a noun form.Building is a noun form of a thing that exists as the result of the act of those who built it.

Light rain because storms had lightning and it started crops on fire or destroyed stuff

Aeolian processes,  pertain to  wind  activity in the study of  geology  and  weather  and specifically to the wind's ability to shape the surface of the  earth  (or other  planets). winds may  erode, transport, and deposit materials and are effective agents in regions with sparse  vegetation, a lack of soil moisture and a large supply of unconsolidated  sediments. although water is a much more powerful eroding force than wind, aeolian processes are important in arid environments such as  deserts