even the slightest alteration to the natural construction of a body leads to a million and four complications...and you almost certainly cant solve them all with conventional logic.
because really, if it were possible/practical it would in all likelihood already exist.
this is a rough concept sketch of how Riyadh's wings work. (or rather, hardly do) the main problem his design encounters is that his muscles would seriously rub against each other with contradictory movements (and therefore be practically useless). if i was being truly faithful to functionality, i would've made his chest muscles and bones like a birds, but that would have compromised his overall humanoid form (which is important to his predominant bloodline, the whynterrfahl).
what i usually do is try my best to make a design believable/accurate, and then anything getting in the way of the defining design elements is scrapped in favor of the vision i have for the character.