I'd need a new top laner...

Definitely Shen. He's hard to kill and has a pretty smooth laning phase depending on the matchup. (Gnar will eat him for breakfast) He's generally a safe pick and scales well into late game.

Shen is more versatile. Every stat works on Shen except mana and mana regen. Malphite is a one trick pony who's sole purpose is to win team fights for his team. But if the enemy team never team fights and opts to split push all the time Malphite's effectiveness is lessened. Shen is the safer bet.

So... Malphite is "only" good in teamfights while shen is better overall. Any build for shen?

Ekko. He's versatile and awesome. I also like Garen, because he's underrated and VERY powerful...or you could just play Teemo.

maybe pick up maokai hes pretty good champ i enjoy him loads and i recommend him hes fun

Riven lel

I got a few Shen builds for you:

Standard tanky Shen:

Build this way when your team needs a tank and you prioritize split pushing over team fighting.

Lighting Shen:

Makes Shen an amazing bursty duelist and the AP makes his shields nearly impenetrable.

Bruiser Shen:

I don't use this one much. But it gives Shen kill potential and well dispersed tankiness.