Active job

New ceiling in one bedroom

I have an older house that has been extended, all the original batten ceilings but one have been replaced by Jib ceiling. I need the remaining bedroom ceiling to be Jibbed, this would leave the existing ceiling in place with the new Jibbed ceiling approx. 3'' lower. I do no require the ceiling to be plastered, as I have other people to do this. Attached photos show existing and expected result.