Besides his name, everything we know about Ori that matters comes not from The Hobbit, but from The Lord of the Rings. In The Hobbit Ori is a non-character, there in name only, and he wears a grey hood.
Drums in the Deep, the Marzabul chapter of The Fellowship of the Ring tells us that Ori accompanied Balin to Moria and survived long enough to chronicle his king's fall and the doom of his people. Ori's writing finishes the fate of Balin, but takes up the story late - he's evidently not in Moria just to chronicle events. It's my conjecture then that Balin took him to Moria for similar reasons to Thorin including him in the Company to the Lonely Mountain - Ori must have other strings to his bow, if you will.
I chose this figure to represent Ori for a couple of reasons: firstly, it is bald (I had it in mind that his remains in the movie scene were similarly hairless), and secondly, it had ample space to add a personal detail - a book for writing in. We know Ori has a good hand for writing, and can write in Elf runes as well as (I assume) Dwarven ones, so the Hobbit movie's assumption, that he is comparably scholarly, is a fair one I think, and it's one I've taken up as well.
But we don't know Ori's age, character or skill at arms. The bow stance gave me room to include the green stuff book and strapping across his chest (there's also green stuff finishing off his beard and right shoulder straps, which are a little unfinished in the original plastic moulding), but all else, as I say, is as much conjecture as Jackson's movie is. I don't think he's a young, nervous, retiring Dwarf (an affectation I think the movie makers heaped on him to ramp up the pathos of his later fate) - but I have no more evidence to back this up than the movie's makers do in creating their version. I do however assume that Ori, present in two attempts to reclaim Dwarf strongholds, has to be more than a mere scribe.
Paint-wise here's the grey cloak as indicated, as well as the described silver belt; plus there's a standard-styled book, rather than a Dwarf-bound one in the movies - I thought that for travelling Ori would be carrying something lightweight and portable, yet robust enough to withstand some rough treatment, so an off-the-shelf volume it is. His ginger beard is, again, informed by the movie. And that's Ori!