Hello I’m having my asbestos roof removed and will be adding new timbers. my partners dad is a retired joiner and will be helping. I just wondered if there was a guide as to how to do it nowadays? partners dad said he wasnt sure if it may had changed since he last did one! He was planning to put 6x2 joists every 600 then 18mm ply on top then put a ‘fillet’ around the edge? (Apologies for any lacking detail) many help greatly appreciated.