If you use a 2X6 fascia for the rakes and the overhang, it will work out OK.
A 2X6 is 5 1/2" wide so if the soffit is 1/2" thick, that adds up to 6".
When you put the roof on, you should use a drip edge on the bottom of the
roof and a rake edge up the sides.
Both these cover 1" below the roof.
This should overlap the fascia by an inch, giving you a nice looking job.

--
JerryD(upstateNY)

wrote in message
oups.com...
I am building a detached garage and want the appearance of 6" fascia
board. Will be using vented vinyl soffit that is about 1/2" (maybe
more) in height. To take advantage of the 6" aluminum fascia cover,
should I use 2x4 fascia so that the J of the aluminum fascia cover can
accomodate the vinyle soffit? If I used 2x6 it seems the aluminum
might not completely cover it and allow for the vinyl soffit. I am
worried about the aluminum not having enough surface area support,
although I guess that would only be an inch or so of unsupport.