Help with roof lining

Hi
I’m currently converting a new (2018) Peugeot expert and I’ve come to a bit of a halt. I have sound deadened and insulated the walls and doors and have also started on the roof. However I’m not too sure how to go about panelling the ceiling. All the videos I’ve seen are mainly of VW’s and they seem to have more cross pieces to screw into.
Has anyone here converted a new expert that can give me any tips on how to batten to fix a ply ceiling?
Thanks in advance