Ridge height under a hip roof?

My roof design has a roof ridge butting into a wall under a hip roof, and the height of that section of hip roof is determined by the height of the ridge under it. So I have two questions:

- How much space should I leave between the very top of the roof ridge and the soffit/fascia of the hip roof? Is there a specific gap there that will make it easier or harder (or impossible) to actually build the soffit/fascia and install the roof?
- Assuming normal building materials (is there such a thing as "normal"?) for sheathing/underlayment/shingles, how much should I add to the Ridge/Top measurement in the Roof Plane Specification dialog box before adding the "working space" (per the question above) to set the final height of the hip-roof above?

I've crawled around those areas of a roof with a hammer many times. 2 or 3' would be nice but it's really and aesthetic thing determined by roof pitch, floor heights and design etc.

A palm nailer will allow nailing in very tight spaces but not every trade owns one.