Soffit size for tiles

[stuartturbo]

Moving forward on with loft but forgot soffit/ over hang for vertical tiles
Intention is to board roof with insulated board with the timber forming the edge. But this give no over hang.
Would fixing a 47mm timber then the 18mm fascia give the drip clearance for a the vertical tiles on 25mm batten. Will be lead apron'd
I know there should be no drips other than of the fascia board.

By the way flat roof

 

[Alastairreid]

You would have a drip detail where the flat roof runs into the gutter.
The sides can be flush with the tiles with tilting fillet on the flat roof to divert the rainwater from the edges and to the gutter....if i understand you right.