Reason #93: building material can be bought from someone’s back yard
Although for some stuff you’ll have to go to one of the proper stores on the island or mainland, some stuff can be bought from “a guy”. Such as this guy’s back yard, offering firewood and roof tiles (special, Brač stone roof tiles).
And how do you know which guy is selling what? There are no classifieds, you’ll see no ads for them. Just ask locals at one of the usual hangouts.