Since bugs only spawn under tiles that have 'Overhead mountain' the easiest way to not get infestations is to prevent any tile like this from existing. (Though that means no deep mining)
As for the person asking about thin roofs, in the past you could designate those as a no-roof zone, then remove the designation, and a constructed roof would be built.
As for the person asking about thin roofs, in the past you could designate those as a no-roof zone, then remove the designation, and a constructed roof would be built.