Cengal (Emas/Batu) is most suitable wood for outdoor furniture in east asia especially Malaysia because of rot resistance (protected by it blood*). Cengal emas more sustainable compare to Cengal Batu (Balau). But you have to spend more penny to buy both type of woods, plus hard to get and off course you need to have suitable tools to handle them.
Good Luck,
Admin
Note : *Yes.., cengal wood got kind of blood inside, some sort of 'resin' or so called 'damar' or 'penak' in Malay Language. The resin will protect any cuts surface made onto it skin or bark. The resin will harden rapidly as to protect the wood. The resin can preserve wood surface up to hundred years.