Hello Jackie, Well the thing about cornice or other details such as dado and or even skirting.. There's many ways to address this from complimentary lighter or darker to traditional white/creamier colours. It takes the ceiling into question too as this can also be complimentary to the walls i.e not white (if there's colour) and spatially too, you can create width and or height in how you address these details coupled with the wall treatments. A lot of people will paint the portion above cornice white or a "white" colour and the ceiling to compliment with the cornice a slightly brighter shade of said "white" colour.. It could be any shade of white to cream but you get the idea. With a modern build and you have no pic here, I would say why not leave it if it's not ghastly.. I do though love the two tone wall which has it's roots in period architecture (It can also be done for skirting where there is none) Now coming, as everything does back into current fashion.. Notice I don't say trend.. Can't stand the word and I believe rather than go with trend you should set it.. With what you like as opposed to what everyone else is doing.. So to perhaps inform you best.. Consider the palette you want to use, light and airy or darker and dramatic and take it from there.. I love to work the woodwork into the scheme but of course what you choose will be what works for you and the space.. : ))

I would have liked to help as could have asked my brother who is a builder, but not sure what you mean, sorry. Maybe a close up pic may help?

I have the same dilema and my extension looks more or less the same as yours. I really want coving as it doesnt feel fnished without it. Im not sure whether to cove up to the apex and stop?… can I ask what you ended up doing please?

I haven’t done this, but I found these examples, although the second pic is mid build.