I am using Randy’s terminology of “roll-your-own” because it’s so appropriate and useful. 
Consider if you will the case of Brian N., a real person of my acquaintance. an intelligent and educated man who, upon his graduation from Calvin College, and wanting to become a Pastor in the Orthodox Presbyterian (OP) denomination, had to face the so-called ‘trial by fire’ to determine his doctrinal orthodoxy.
He faced a group of elders and leaders and was orally quizzed on a number of items, the focal point being his agreement with everything in the Westminster Confession.
With one small quibble that was not judged fatal, he did so agree and went on to neither fame nor fortune, but a satisfying (it is to be hoped) ministry.
Something like this is no doubt common to most denominations. (an interesting word: "… a name, designation, or title;** especially, a general name indicating a class of like individuals; a category**
(countable) A class, or society of individuals, called by the same name; a sect or religious subgroup: - Wiktionary - my emphasis)
It seems clear that each ‘class’ considers itself Orthodox, even if that word is not used to designate the class; orthodox in the sense that, out of the abundance of Revelation and tradition and church history and all the things written about it, this class of people has CHOSEN a set of propositions as those elements considered to be most faithful to said abundance; primarily, of course, to Sacred Scripture.
Is Orthodoxy ‘roll-your-own’?
Yes it is. It appears to be a self-sufficient, established, concise, Scriptural body of belief but:
-it was put together by men, each of whom chose what to believe out of the abundance of materials available at that time and
-the materials that were used were previously produced by men who made choices that were often contradictory to one another and
-the church Councils also made those choices (and if you have not read the histories of those Councils, you should, to see how the ‘sausage
was really made’)
There are books written on these subjects. Let me just say that from what I’ve read and observed, Christianity is not ‘tidy’. There is nothing 'pre-pakaged. If you are Ox of one stripe or another, or Anglican, or RC - and consider those not of your persuasion to be somehow deficient (or heretical, God forbid) by their picking and choosing what to believe - really, look in the mirror. We all do exactly the same thing, as did those before us, and before them - unless we are calling for blind obedience.
I think for the 21st century individual the following is unavoidable:
"God said it.
I interpreted it
as best I could in light of all the filters
imposed by my upbringing and culture,
which I try to control for but you can never do a perfect job.
That doesn’t exactly settle it
but it does give me enough of a platform
to base my values and decisions on."
