Opening up roof/ceiling space

Hi
we have just had a builder in to quote us on our kitchen to re plaster etc. The kitchen is a kind of add on to the back of the house, single story with pitched roof.
What we were looking at is removing the horizontal ceiling to have velux windows installed. Our builder advises he would just remove the ceiling joists and add nogins between the rafters. Is this correct? As far as i am aware a pitched roof naturally wants to collapse like 2 cards leaning together and you need some sort of binder attached to either side of the pitch.
Hope this makes sense, not sure of the correct terminology!

he might put collars on them

mnasure the timbers width, depth and length, and their spacing, and the room size, and tell us. One of the chaps who knows how will know what you can safely do.

Don't let the builder cut them off without giving you a dimensioned diagram of what he plans, or, as you say, the walls will fall down. This may not happen until after you have paid him.

p.s. with no insulation, that ceiling is going to be extremely cold, and will suffer badly from condensation.

How to build the moisture barrier, insulation and ventilated gap will be another question, though.