Welcome to the Bunnings Workshop community @Muzaffar and thanks for making your first post. We look forward to reading more about this project and many others you might have planned around the house and garden in future. Our helpful members are always on-hand to provide any help and inspiration you might need.
I'm sure one of our resident Bunnings D.I.Y. experts such as @EricL will be happy to share his thoughts to assist you, but I wanted to let you know that we had a similar question to this recently that you might find helpful: How to attach shade cloth from roof side to Colorbond fence?
Bunnings has also produced a step-by-step guide how to install a shade sail. The video can be found below.
And as per the advice in How do you install a shade sail, I would also like to remind you to please seek professional advice on what posts to use and how they are installed as the force on a shade sail can be significant. In the Bunnings guide, the installation of the three steel posts was overseen by a qualified builder to ensure they were structurally sound.
Hope that helps kick off the discussion,
The Colorbond fence material and structure are not strong enough to hold the force generated by the shade sail when wind and rain are striking it. Attaching it to your roofline is also not recommended as again the material is not strong enough to withstand the forces generated by the shade sail. You'll need to use a post in each corner to properly anchor the shade sail. As mentioned by my colleague it is best to engage the services of a registered builder to make sure that the posts are anchored properly in the ground.
The common materials used are either timber posts or steel posts. There are many types and sizes when choosing the shade sail itself, please pick carefully what size you'll be putting in. The most critical part of the assembly is the tensioning system for the shade sail. As time moves forward the straps and shade sail itself get stretched and expand. This then produces a droopy sail, in order to combat this, I suggest putting in Coolaroo Shade Sail Turnbuckle to tighten the straps without having to disassemble the shade sail. In this manner, your shade sail will always be nice and straight.
If you need further assistance, please let us know.
I'm glad the information helped. Please keep us updated with your progress, we look forward to seeing the start of your shade sail project.
If you have any other questions we can help with, please let us know.