Shiplap roof advice

[Hippygaz]

Hi all
I built a shed a few years back with the roof out of shiplap . The job looked good when I finnished , but is now deteriorating - shrinkage , wrong thickness timber ..
I'd ply and felt it .. But wife - being the arty type - insists on shilap .. Anyhow in going to use 7" 20mm thick , pay more attention to the overlap and fixing and make sure it's pressure treated etc .
My question is this ...
The shed is going to be used as a workshop , so the idea is to use one of these methods
Breathable membrane across rafters then 9mm ply over this then feather edge straight on top ?
Or ply over rafters .. Membrane on ply then featheredge ?
Ply - membrane - batten - featheredge..
The last one feels right , but feels over the top ...
Or am I just over engineering it ..
I would also be redoing the walls with either of these methods .

Should I bother with the ply ? Seeing as I'll be lining inside ?

Also Best ,economical way to seal the ridge line ? Construct timber ridge tiles ? Could someone advise me on construction if these or better alternative.

Many thanks in advance . As any ideas would be greatfull ..

 

[Hippygaz]

Sorry I meant featheredge .

 

[foxhole]

I would use osb internally, cheaper and allows fixing shelf etc.
Feather edge board is not ideal for a roof unless it has a fairly steep angle.?
Piece of upturned guttering will seal the ridge line.
If it were mine I would be looking to use EPDM, one piece and hard wearing and water proof.