The trusty old corrugated iron roof is synonymous with New Zealand architecture and of course they aren't all made equal. Along with the various gauges (or thicknesses) there are quite a few options in materials, coatings and colours. Like house painting do your researchNow by now you know I'm going to say - buy quality.
In my experience its not worth going a mid priced job, you either do the whole job properly using quality long lasting products or you get your building maintenance company to perform roof repairs or house painters to sort out your roof.
A good roof painting job will give you 10-20 years extra life where a re roof using at thick gauge galvanised steel, will give you at least 50 years if not more depending on the material used and how well the building maintenance is carried out.
The below list covers some of the corrugated roof range in New Zealand
Corrugated galvanized steel.
The original product was wrought iron– sheet steel zinc coated, then roll formed into corrugated sheets. This product is still commonly used today in New Zealand. Modern architecture and "green" thinking has made these products popular again.
Zincalume and Galvalume
A blend of zinc, aluminium and silicon-coated steel, Sometimes left in the raw zinc finish, but more widely used as a base metal under factory coated colors and sold as Colour steel. No house painting required
Metal tile sheets.
These are usually painted or stone-coated steel. Previously sold under the name Decromastic
Available for harsh conditions and/or as a distinctive design element. Usually roll-formed into standing seam profiles; however, shingles are available.
One of the longest-lasting metals, but somewhat expensive compared to steel products. Aluminum roofs are very lightweight, corrosion-resistant, have high natural reflectivity and even higher natural emissivity, increasing a building's energy efficiency. Aluminum products with Kynar paints easily last over 50 years. The newest innovation is anodizing of the aluminium coil stock for use in architectural details and standing seam panels. The anodized layer is intimately bonded the metal and is not normally subject to weathering and wear.
Expensive for a roofing material. Usually used for flashing or smaller, highly detailed areas such as entrances of historical buildings and churches.
Stone coated steel.
Panels made from zinc/aluminium-coated steel with acrylic gel coating. The stones are a natural product with a colored ceramic coating.
Inverted Box Rib, Trapezoidal or IRB.
A low-cost corrugated square-fluted iron roofing material used mainly in the commercial market. It can be commonly found on anything from industrial sites to low pitched roofs.
A metal roof graded "AG" or "Utility" will need re coating (roof painting)once the factory finish wears off, or corrosion will occur. These paints are commonly acrylic or polyester based. Roof coatings are the preferred material since they are able to stay elastic and withstand the thermal cycling that occurs in metal roofs.
Roofing materials made from stainless steel, zinc or copper will rarely require maintenance over their lifetime. Any required maintenance is usually due to design or installation mistakes. Otherwise, these materials commonly last over a century.
Metal roofing with long life polymer coatings like Kynar should not normally require maintenance until the coating fails. These products have been used for over half a century now in the U.S. and few installations have failed. They should be considered lifetime products.
( Note some excerpts from Wikipedia)