Trundle top is solid if you're aware of his strengths and weaknesses. I'm not a fan of him in top lane and I much prefer using him in the jungle, but that's irrelevant here.
Anyways: generally speaking you don't want to pick a fight in the earliest of levels if the opposing laner does a decent job of trading back (like Renekton), so focus on farming and sustaining yourself if you take any damage. Once he's approaching level 6 you can start being more aggressive if you want and against most common top lane champions he'll do fine if not outright beat them. Ranged laners are a nightmare for Trundle top though: he has very little chance of ever touching the likes of Lissandra, Karma and Quinn without jungler assistance based on my own experiences. Don't ape the solo queue / LCS bandwagoners who blindly buy Blade of the Ruined King and Sunfire Cape (which is garbage) on him at all times; BoRK can be great on him, but not so much if you're struggling to auto-attack anyone (much less a high-priority target) at length. Another valid option for him with regards to offensive sustain is Hydra; it enhances Trundle's already potent split-pushing ability - by default he needs little time to whittle down structures on his own - and you'll be able to stay alive for longer if you intend to jump into the fray with multiple enemies surrounding you. If you're uncertain which lifesteal item to buy, then you can always stick to a Vamp Scepter and focus on buying a Trinity Force for increased damage in the mean time, which has fantastic synergy with Trundle. Spirit Visage is the MR item for him, alongside Hexdrinker / Maw of Malmortius to a lesser extent. Not a fan of Iceborn Gauntlet on Trundle (even if it's not bad for him per sé), Frozen Mallet can be alright if you'd rather be the tanky frontliner with loads of peeling / chasing potential, Randuin's Omen is a no-brainer, Thornmail can be decent and that about wraps up your obvious itemization choices. Stark's Fervor (or Zeke's Herald) is a situational pick-up for when multiple members of your team deal AD damage, and it allows you to be an obnoxious prick with Pillar spam.
Speaking of his Pillar: the minor knock-up on it is actually quite handy to abruptly cancel certain mobility skills like Shyvanna's, Tristana's or Jax' jump if you time it right, further increasing its versatility if you get the hang of it. Pillar allows you to help defend towers, greatly delay the follow-up of an enemy engage, continuously chase if you have the CDR for it, start sieging with relative ease alongside poke champions, safely check bushes thanks to its cast range and the vision it provides et cetera. It'll take a while to acquire an understanding of when and how to use this skill 'correctly' though, but that shouldn't be a surprise with a flexible tool like Pillar.
Given that you have played Ryze a bit in top lane, I'd suggest trying out Karma too. While not inherently beefy with her itemization (comparatively speaking), she can be deceptively resilient nonetheless thanks to her shield + Empowered W (the snare). Her cooldowns are fairly low, she has a noticeably stronger laning phase than Ryze against the typical melee top laner and she transitions well into late game (albeit differently) thanks to her overall utility. Her Empowered Q can hit hard, but mind you that it can be intercepted by minions or champions alike.