First, Ghost is mandatory on Olaf. It has a lower cooldown than Flash, it allows you to chase enemies under your tower (or theirs if you're fed enough) and reach the enemy backline during fights before dying heroically (or not)
Also, Since we are playing with Unsealed, TP is fulfilling 2 roles : It allows us soaking the potential early pressure because of the lack of Conqueror, and we can efficiently roam while still preserving our summ advantage.

STARTERS

Doran's Shield is our go-to option : since we don't run Conqueror, Triumph Last Stand, nor ignite, we can't cheese the enemies in their CS at level 1.
Instead, playing safe until level 6 with our passive is much more efficient, since it allows us going for an aggressive ghost+ignite/exhaust and ult on the opponent, while we will likely be farming under turret.

Although Doran's Shield is a very good item for our strat, it is useful only if the enemy laner plans on threatening us early game.
If that's not the case, the long sword + refillable start already grants us 410 gold for our Eclipse rush, and allows us to rush an early Doran's Blade if we need it.

CORE BUILD

As you may (or may not) have guessed it, this build highly revolves around cheesing our opponents with unexpected survivability, lots of teamfights, and last but not least, spamming items effect every 4 seconds instead of 6 with Ingenious Hunter.

Eclipse and Sunderer Sky both have a massive advantage in that regard : they both deal damage and grant you a heal or shield. This creates a massive difference, and a single additional proc from both of those items can create a 600 damage difference.

Sterak's Gage every 40 seconds is absolutely nuts in late game, where your help can be needed 24/7. If you rush a Malmortius, it's often best to build it as early as can be (for annoying AP champs such as Rumble or Vladimir), but it is also a great third item.

Although its passive has no gain whatsoever from Ingenious Hunter, Experimental Hexplate gives you even more uptime, as you can either pair or cycle it with ghost so that you're a threat at all times of the game for the enemy carry.

BOOTS

For our boots, Swiftness Boots are the only viable choice here. Outrunning everyone, deciding when to take a melee trade or not, is just too good of an advantage to pass on it.
Moreover, although it may look like slow resistance isn't good on Olaf because he can cleanse it with R, you are generally going to wait until the enemies throw their hard CCs before engaging them, so it still has plenty of value.

We dont run Lucidity Boots because Ability Haste isn't that good of a stat on Olaf (Q doesn't fully benefit from it, and neither does E + ult is already reduced by Hexplate), and we already run Unsealed Spellbook which massively decreases the effectiveness of Summoner Spell Haste.

LATE GAME

For your last item, it's the moment where you can get as creative as you want :

Depending on the gold that you have, the build paths of the items, the enemy comp and the fed carries, I think you can pick any of those items. Most of them benefit from Item Haste (especially given that Ingenious Hunter will likely be fully stacked at this point) and are here to either grant you survivability, or make you a nuisance for the enemy team.

Dead man's Plate for movement speed+armor

Anathema's if they only have one fed enemy (especially if he deals mixed damage, PERFECT against katarina)

Black Cleaver if your team is full AD and the enemy team went full armor to counter this

Death's Dance if you get one-shot

Frozen Heart if the enemy carry carries a bit too hard

Hullbreaker if you plan on ragesplitting until the end of the game (especially if you're too far behind)

Iceborne for perma slowing the enemy team and allowing your team to land skillshots

Jak'Sho if the fights are long, and the enemy comp has mixed damage

Kaenic Rookern against full AP

Profane Hydra if the enemies are deletable, and you have enough vision to try killing squishies in one combo

Randuin's vs full crit teams (GP Kindred Yasuo Jhin Senna)

Shojin's for... hit strong

Spirit Visage if you have a Karma+Soraka or if Yuumi sits on you + Enemy team is AP

Stridebreaker for slowing in teamfights

Trinity for... hit strong, but every second with Ingenious Hunter

Last but not least, Unending Despair can have tremendous value if the enemy team doesn't have executes and basically make you unkillable for the whole game

MAIN RUNES

Unsealed Spellbook is insane on Olaf : it will define your whole playstyle. Instead of just splitting and praying so that your team doesn't die 4v4, here, you will use your perma summs uptime + surprising low hp tankiness (Ingenious+Sundered+Eclipse+W) to just roam around the map, help your team get some plates, run on the enemy ADC super soon and catching the enemy jungler while he farms.
Although this could arguably make your laning a tad harder, this is greatly compensated by the fact that you literally don't care if you lose lane. If the enemy toplaner has 1 level + 1 item advantage at 35mn but your whole team is 10/0, this won't be a problem at all.
There are a lot of things to learn while playing this rune so it's ok, don't forget that Exhaust makes you proc approach velocity and you can get high ranged damage with Q+ignite+eclipse proc !

Boots for 300 free gold, you slow the enemies + ghost if you wanna all in them early on, you get extra MS when it procs, and you can often get Eclipse before the 10mn mark, it's literally awesome.

Biscuits are perfect for sustain + free harass with axes

Approach Velocity gives you so much MS it's stupidly good on Olaf, makes you reach the enemy carry in no time (as long as you hit your axes)

Eyeball Collection gives us some snowball potential, but it can be switched with ghost poro or zombie ward depending on which trinket you wanna use (I personnally prefer sticking to the Stealth Ward)
Ingenious Hunter's value is absolutely insane and our whole build revolves around it.

As for the mini runes, AD>AS on olaf (he has no on-hit effects, only some lifesteal which also happens to scale off his AD)
In my opinion, Scaling HP > AD since this can save you a lot of times in late game and scale with your W
And HP > Scaling HP to have more overall survivability early on.

ALTERNATIVES

Although Triple Tonic seems really great on paper (free early golds, easier farm, perfect level 6 all in with an extra summoner spell, great value from Elixir of Skill as Q/W/E all scale really well from levels), it can often lead to you having too many items (DShield, 3 long swords, Refillable Pot, Biscuits) and be hard to manage. Also having to pay 300 gold for boots is annoying.
That being said, it's really nice in matchups where you will want to rush boots ASAP (Swiftness for Mundo, Tabis for Trynda etc)

Minion Dematerializer can be great if you're good at wave management and if your game plan is clear.

Also, Future's Market can be paired with Magical Footwear and a Long Sword Start for an approximately 900 gold cheaper Eclipse.

Cosmic Insight is perfect on paper, mainly because of the Item Haste, but Having to pass on Approach Velocity makes you feel like you're playing as a tractor. Not recommended.

Cheap Shot is very good if you want to play super agressive early game, as it can quickly add up to 200 true damage pre 6.
Double AD mini-rune can also be good in free early matchups.

Ingenious Hunter has way too much value not to be played atm, because items are broken in S14.

If you go Conqueror + Ingenious hunter, you end up having to pass on the Inspiration Tree, which was insanely good on Olaf.
Then, you have to use the overnerfed Conqueror rune and choose between Legend:Alacrity and Legend:Bloodline which both don't synergize very well with Olaf.