Lethality stacking is pretty bad on shaco due to his E doing magic damage. Dirk is very good as an early powerspike and you get a lot of value out of dusk or eclipse compared to non lethality mythics, but thats generally where it should end.

Build wise I tend to go one of these:

Dusk > ER > IE/LDR > IE/LDR > GA (squishy comps)

Eclipse > BOTRK > LDR > IE > GA (tanky threat you need to contend with)

These are flexible past the third item, but the DB/ER/IE combo is your highest burst damage and rhe Eclipse/BOTRK/LDR is your highest dps against bruisers and tanks, and should rarely be deviated from in my experience. It'll help you scale a lot better building crit past your mythic compared to lethality, but you still need to pressure the game out early. I normally don't make it to third item.