Help required for a novice woodworker - I've spent quite a while designing a fort, but have struck trouble trying to work out what timber is best to use to build it. The fort will lie on top of a concrete / slate slab, no footings will be used.

I'm not keen on treated pine with CCA, but ACQ would be fine. Not sure where to get in SA? Any ideas? How much dearer is it than CCA?

I am open to other suggestions too - considered cedar, jarrah and cypress pine. Are these good options? How much dearer though? Is the secondhand salvage yards typically a good option for buying this?

Any help appreciated. Was hoping to get timber ASAP and build before Xmas!