The grey on the western wall looks dark and purplish on my monitor. It may come over as too imposing and monolithic on the southern face. If you're sticking with the grey palette then a warmer tone would suit the sandstone better. Does Dulux have a colour palette recommendation that includes your Berkshire White plus a grey? Check online or in store pamphlets. But, for such a big, expensive, and impactful paint job I would actually be tempted to get a colour consultant. You're not just repainting a loungeroom wall if it doesn't work!

Terracotta roof tiles. Then you could either go with steel greys and blues, varying shades and tones of terracotta or a combination of both. Have included some Dulux colours showing how versatile terracotta can be to perhaps give you some inspiration...

I think its too dark , too grey , and that the darker tones don't show off the Merbau timber well ( or vice versa ) . Personally , I think either go lighter on the walls ( surfmist or similar ) , keep the monument roof , then a bright colour on the trim and entrance and garage doors -- red , orange or yellow are my favourites , but on your design it may make something nice look a bit too 'slapped together transportable building' , and in fact almost any colour may suffer that fate , so how about a rock look for the base , rather than timber ( whether you are going light or dark or natural , it could look like its just waiting for someone to knock off those base timbers and back a truck under it ) . The other combo that may work would be your darker colours , but have varnished light beech or similar for the base , decks , even the entrance door and garage door ? Basically , someone going to the trouble of varnishing looks more permanent than anything that looks like it is or could have been stained IMO .

Dulux colours. Dark colour Dulux Oolong, Dulux Ticking. Light colour Dulux Casper white, Dulux snowy mountain.