Function build 

pub fn build(
    entries: &[DataEntry],
    files: &[(&[DataEntry], Option<u32>)],
    linkage: &[DataEntry],
    local: &[DataEntry],
) -> Result<Layout, Error>

Lays out WORKING-STORAGE, then each file’s record area, which all its 01 records share and which is at least record_max bytes.