Here's what to know about this particular build:

1) I used to play Trundle with much more defensive items early on, and that's just no good. You loose all your momentum and threat capacity, and simply become an unkillable target to wrongly initiate team fights later on. By starting offensively, you stack your damage, stack the kills, the money, and THEN build your tankiness.

2) This build revolves around the Use of the Devourer Jungle Item. It May be possible to use the warrior enchatment instead, But you may want to reconsider using the Black Cleaver at all.

3) Trundle is all about stealing the opponent's stats, were it be Ad with his Q, or their defense with his ult. The goal is to build items that reinforce that philosophy, like B.O.T.R.K, The Black Cleaver, and Randuin'S Omen.

Enjoy and feel free to comment!

All I have to say about farming is that you will want to disappear in your jungle once you bought the Devourer Enchatment. An Ideal stack completion happens around 20:00. It that sense, you might want to make a quick but usefull gank around Lvl 3 or 4 to one particular lane that needs early ganks, because you might emerge only very later, when the laning phase is almost over.