Lining the lake house ceiling

Dad is pressing on with work at the lake house, whenever he can find a spare couple of days.  Now we have a roof on both sides, and a start made on lining boards holding up the insulation too. I love the way it looks, it will be brilliantly airy and light feeling.

Email from Dad, Nov 13th:  (originally we'd planned to leave the lining boards as a job for us to do)
I want the best lining boards to go on the old house veranda... that means that I will possibly have to use several different types of boards to do the lakehouse. I have realised that if I don't do this task now I will have to provide another 4 rafters for the task of fixing the ends of the boards and that is pointless. So I will do that task now.

 Email from Dad, Nov 26th: 

I sorted the boards of several of the most promising board size with respect for quantity to complete the work with one type of board. This was worthwhile work as I needed to be sure before committing myself to a size. As it transpired I have a sizeable pile, I think I will get all the dado as well as the ceiling from it. There are very many boards which almost work-in but don't because of the ends being split or rotted. These will be cut to use for the dado up to 900mm. Above this dado will be plasterboard painted to provide the contrasting and set off the lining boards.  I didn't straighten the underside of the rafters as when I checked they were pretty good on this side at least.