In Victoria, roof work splits by material. Anything metal, anything that carries water and every flashing is plumbing work: Colorbond and galvanised sheets, valley irons, apron and step flashings, penetration flashings around pipes and vents, gutters, downpipes, box gutters and rainheads. Those jobs are carried out by licensed roof plumbers. Tile work is different. Replacing a cracked concrete or terracotta tile, rebedding a ridge and repointing it with flexible compound is roof tiling, and it is done by experienced roof tilers.
Most Melbourne roofs need both trades at some point, and plenty of single leaks involve both. A rusted valley iron under a tile roof is a plumber replacing the metal and a tiler lifting and re-laying the tiles either side. A skylight set by a tiler still needs its flashing done by a plumber. A storm that lifts a ridge cap and tears a sheet off the carport needs one visit, not two quotes from two companies who each blame the other.
The office works out which trade the job needs when you describe it on the phone, and sends the right person. If you would rather understand the split before you call, the roof plumber Melbourne page explains it in plain words. What you will not find on this site is a claim that one person does everything, because on a roof that is rarely true.