Olaf needs to be tanky to survive teamfights, it's best to just build him full tank and use your crazy high base damages and movement speed in teamfights. Building devourer simply means you won't be tanky at all till you get at least 3 full items and means you're just so much weaker in teamfights.
I agree with Vynertje on this and the only offensive items I would consider on jungle
Olaf would be :
Hope this helps you out.

Black Cleaver - (This item gives you a lot of stats that
Olaf likes - MS/HP/AD and it works very weill with
Enchantment: Cinderhulk)
Blade of the Ruined King - (Helps cutting down tanks and the active is really nice for chasing people down/setting up an easy
Undertow)
Hexdrinker - (I would probably rarely, if ever, build this, but it can be a solid offensive option vs heavy AP teams)
Hope this helps you out.

If you have any questions, feel free to PM me.
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Do you think some other approach would be better and if so why?