Hi Brett about 5 to 10 years ago the trend was if your design style was contemporary your trim colour was the same as the walls and if your design style was classic your trim was a lighter, often white contrast to the wall colour. These days the trend is to the latter regardless of your design style as your builder's designers suggested. However matching your trim colour to the walls is still a good option if you have 8' ceilings. As there is minimal difference (only in the level of sheen) between the skirting boards and wall colour it makes the ceiling look higher. Another option is to do the trim in a similar but lighter tone such as Dulux Grey Pebble quarter. This is a very subtle tone on tone look. Whatever the colour, do you have a choice in the sheen level for your trim? I generally recommend semi gloss enamel on trim unless you are after a more classic look and your woodwork is in very good condition (the higher the sheen level the more any imperfections show up), in which case you could consider full gloss enamel. At the end of the day it's your home so you should do what you'd prefer - after all it's only paint so it's easily changed! All the best with your build.

I'd paint all the ceilings with a flat ceiling white.

I had similar dilemna and painted all woodwork including doors etc white, which I am happy with, it all ties together well.

I don’t want to paint the beams I want to paint in between them but as my walls are beamed and the ceiling is vaulted I don’t know whether the whole room has to be painted the same colour or I can paint the ceiling one colour and do the walls in another.