It's very difficult to estimate the life of a western red cedar shingle-clad wall in the Melbourne climate, since it depends on weather exposure (whether there is any shielding), roof overhangs if any, maintenance of a finish and similar factors. However, some general observations might help. Timber-clad walls survive best when water runs off without being trapped. Western red cedar is a durable species and is rated Class 2 outdoors, above ground, according to Australian Standard 5604:2022, Timber - Natural durability ratings.

WoodSolutions is purely an advisory body and we don't produce timber products, so we would not have a use for your blackwood. Its marketability will depend on a number of factors including the quality of the logs, for example whether the trees were pruned to produce high quality 'clear' (knot-free) wood. Other factors include whether you are located near a sawmill, preferably one with kiln-drying facilities, how many trees you have, accessability of the site to harvest the logs and so on.