The ABCB Housing Provisions don't specifically deal with damp-courses under timber frames. The assumption is that they will be used in brickwork or under concrete slabs. However, it can be a useful precaution to place a damp-course under the outside wall of a timber frame that is seated on a concrete slab. While problems rarely arise if no damp-course is present, occasionally slabs are subject to edge dampness.

Supplement no. 5 to Australian Standard 1684.2-2010 for non-cyclonic areas tells us that in N1/N2 wind areas 190 x 45 MGP 12 rafters @ 600mm centres will span 5.3m. That's for a single span (supported only at each end).

WoodSolutions Technical Design Guide #04, Building with Timber in Bushfire-prone Areas, is currently under review. However, a 'generic' tiled roof system (ie. one not restricted to particular brand-name products)  is included in Appendix H of Australian Standard 3959:2018. We will send you an extract from Appendix H under separate cover.

We weren't sure if you were looking for suppliers of cross-laminated timber, or design professionals. Suppliers are well represented on the net and you will find them if you write "Australian CLT suppliers" or similar in your browser. Details of local CLT projects are also available on the net such as Forté Living in Melbourne, more info here: https://builtoffsite.com.au/emag/issue-04/forte-living-australias-first-multiresidential-clt-building/.

There are many building inspectors on the net who offer a professional service. In heritage matters we have had good reports about Richard Forrester, formerly an inspector with the NSW Forestry Commission. You can access his website via this link https://paragonengineering.com.au/team-member/richard-forrester/, phone 7227 7775, mobile 0429 646 112.

We assume the alfresco ceiling won't be exposed to the weather in any way. All species of timber react to gaining or losing moisture by swelling or shrinking. If the timber is in a stable environment, tongued and grooved lining boards are available in a number of Australian species from companies such as Austim. You could also consider V-joint plywood or 'engineered' flooring, depending on the appearance you are looking for. Engineered flooring generally comes pre-coated which could be an advantage when installing a ceiling.