tilt batten question
 

Hi all.
I am replacing the rotting facia boards and soffits in plastic on my 1970s
concrete tile roofed bungalow.
Its my first d-i-y roofing job and its proving to be a straightforward job
apart from our Scottish rain.
The roof is boarded in the dreaded Cellatex cardboard- roofers must have
fell about laughing when they saw that stuff in the 1970s untill they
realised yes they really were going to put cardboard on roofs!!!!!!!.
My roof is made up of single lap concrete tiles close boarded and sarked
with hessian felt the last foot of which has rotted away the cellatex is of
course lying in bits in the soffit box rotting the facia fortunately not the
truss ends.
I am replacing the boarding with cladding 9mm plywood and the sarking with
DPC .

Question 1
can I replace the Cellatex tilt batten with an aluminium strip--I am
fitting eaves protection.
Question 2
must the edge tile sit on top of the plastic facia or is it advisable to set
the tile higher.
All relevant comments eagerly awaited.