This is a boss status Tryndamere build. Although the item build is a little complicated its totally worth it once you get it down.

Most people are under the impression that having Critical Strike Chance runes are the way to go under the assumption that more critical strikes = more damage. After some digging I've noticed critical damage runes and quints are more effective mainly because you cant get critical damage items in game. That being said with Infinity Edge you can pull off 280% + critical strikes. That's some serious burst damage and that's what you want. Flat CDR runes are the way to go too because with blue buff you'll have 2 second CD's on E and 5 second CD's on Q making you nearly invincible with a great escape mechanism.

!!WARNING - MATH!! Flat CDR > CDRpL and HPpL > Flat HP

The best comparison between rates and flat runes is the ratio between them. That ratio will give you the level at which the two runes equal one another. Above that level the per level rune is better, below the flat rune is better.
- Flat CDR (0.65) / CDRpL (0.05) = 13. At Level 13 your CDRpL equates to your Flat CDR.
- MAX Flat CDR: 9 * 0.65 = 5.85%
- MAX CDRpL: 9 * 0.05 * LvL(13-18) = 5.85%, 6.3%, 6.75%, 7.2%, 7.65% ,8.1%
- Comparison: Assuming a 5 second CD ability, Lvl 18: 4.595s for CDRpL vs 4.7075 which isnt much difference. BUT at Lvls 1 - 12 5.85% CDR gives a lot more survivability given you'll definitely have less items at this point.

HP: Using the same principles as the CDR, Flat HP / HPpL = 5.35 / 1.08 = 4.9 ~ Lvl 5. By LEVEL 5 HPpL SURPASSES FLAT HP... Need I say more?

This build incorporates a double tier item build. The first tier or "Core" items are:

Doran's Shield - Cloak and Dagger - Vampiric Scepter - Boots of Speed - Brutalizer

Doran's gives nice tankiness for early levels as Tryndamere is pretty weak early game. Cloak and Dagger is like a mini Phantom Dancer; get this **** asap. It's pretty much gg after this assuming your team doesn't suck. Vamp Scepter gives you a little more survivability plus allows you to keep Bloodlust stacks up instead of using them to heal so often. Brutalizer is the icing on the cake. Armor Pen, AD, and 10% CDR??? GTFO!

Second Tier and Final Items:

Black Cleaver - Warmongs - Phantom Dancer - Stark's Fervor - Zerk Grieves - Infinity Edge

Don't build in this order ofc. Most of the previous items are sold for there upgraded versions.
- Cloak and Dagger -> Phantom Dancer
- Doran's -> Giant's Belt -> Warmongs
- Vamp Scepter -> Starks
- Brutalizer -> Infinity Edge

Normally I upgrade to tier 2 in this order:
Zerkers, Starks, Giant's Belt, Black Cleaver, Infinity Edge, Phantom Dancer
This is because Starks and BC give you some nice ARMOR REDUCTION, not ARMOR PEN. This is awesome because it can bring your enemies LOWER than 0 Armor. This allows you to RAPE people quickly. Plus they give you some nice Attack Speed which stack with the Life Steal from Starks and Crit chance from the passive and Cloak & Dagger.

Note: Every time I upgrade I sell my tier 1 item. Items sell for 70% of the original cost except Doran's (50%) and Gold per 5 items (50%).

Many other guides say to first max Blood Lust, then Mocking Blow, then finish out Spinning Slash ofc getting Undying Rage whenever you can. I disagree, respectfully of course. Tryndamere's most important ability is his ultimate but I prioritize:

Blood Lust > Spinning Slash > Mocking Blow
BUT no more than 3 points in Spinning Slash prior to pumping up Mocking Shout and Max Blood Lust first. This is because early game the slow on mocking shout is useless considering Trynd's solo DPS is really Item dependent. Due to this Spinning Slash gives you some really nice farm. Check out the Tips / Tricks section for more details.

Farming: Spinning Slash into the mob, lowering the group's HP by nearly 50%. Two hit the back row giving you at LEAST 4 - 5 stacks of blood lust. At this point your Spinning Slash should be off CD. Slash through the heavier minions and finish them off with full stacks. If you're being harassed during this, just heal off your stacks you gain from kills.

Ganks: Low on Stacks? Pop in and kill a few low hp creeps first. You'll gain stacks off hits and 1 per kill. Exhaust the enemy and Auto Attack Nuke them down. Remember the more stacks you have the more crits you get so starting out with 0 stacks attacking an enemy you might not snowball crit.

Wall Jumping: Probably the most important move Trynd has. You can use Spinning Slash to go through a lot of different walls around the map. This is a great way to escape or initiate ganks.