Welcome to the Bunnings Workshop community. Thank you so much for joining us and sharing your question about what materials should you use for decking over your concrete slab.
My first suggestion is to have a look at this excellent guide - How to build a low-level deck by @Adam_W. In it, you will find the basics of how to build a deck. It will also give you an idea of how to make your own plan. Using Treated Pine Outdoor Timber Framing 140 x 45mm is definitely an option for your decking frame. Using Ekodeck is a great investment for your deck. Once you've made your plan make sure to post it. Our members would be more than happy to provide you with advice and information.