[CrateCruncher]

I recall the other thread degenerated into a problem about answering such a generic question. I personally tackled hinging doors by breaking such a large problem down into more bite sized pieces:
How do you cut out body panels?
How do you fabricate a hinge?
How do you mimic the articulation of the prototype?
How do you fabricate missing detail parts like door jambs, weatherstripping...?

After acquiring the skills to tackle each of those problems I found I could develop a hinge for any door, hood, sunroof, engine cover I wanted.