A low-pitched roof is often very attractive because the lines can be long and add shape to a home. However, they come with special needs that are easily catered for if a little thought goes into their building and roofing.
The pitch of your roof (how steep your roof is) determines how quickly and easily water flows into your guttering. e.g. a flat or very low-pitched roof will not move water as fast as one with a steep pitch. This could cause water to flood into the ceiling when rain is heavy, such as during a typical Brisbane storm.
If you have a low-pitched roof (less than 5 degrees), then you need a roofing profile that has high ribs because these are specially designed to deal with this problem.
The rule of thumb is: the lower the pitch, the longer the sheet, the higher the required profile. This means that having a short flat roof is usually not a problem (e.g. a patio roof can probably cope ok with heavy rainfall), but if the flat pitch extends for a long way, you are essentially building in a leak.
Ways to deal with this problem is to either rebuild your roof trusses so that the pitch is increased, which is very expensive, or use the correct roofing profile. For example, Trimdek or Cliplok have higher ribs in their steel sheets than corrugated iron and so they are perfectfor this problem.
The gauge or thickness of the iron is also very important. Because of temperature variations, metal contracts and expands thousands of times a day. After it has done this for several years, it will eventually cause a slight bow in the sheet, allowing water to pool. Once this starts happening, rapid deterioration of the coating of the metal will occur. This mostly occurs when the purlin span is too wide, so if you are building a house, speak to your architect or builder about making sure that they are the recommended distance apart. To counteract widely-spanned purlins that are already in place, use a heavier gauge profile.
Steel is enormously strong and versatile, so with a little thought you can make it successfully fit any roof.