Predecessor Builds > Morigesh > Mori Roaming Mid
This is based on Armageddons Swamp Queen build, and that build gave me a comfortable foundation to play. If you want a great mori build, start there.
I've started using Mask as first item for the even spread of passive stats, the % increase to magic power in lanes scales nicely into midgame, and the mana back on kill is not insignificant and gives me an option to hold on Caustica if I don't need to blast through tanks and gives me an option to grab that third item based on team comp.
The current third slot is a flex spot. If tanks or mana are the issue, grab caustica here and let the fourth be your flex spot.
Ideally, mask of amir, into wraith leggings, into world breaker, and your damage scales so hard as each of these items increase magic power by a percentage. Mark and hive and ult anyone not building magic defense.
Because of that % magic power scale, try to be in lane when you ult for that juicy 8%.
Of course, crest depends on the match. If I don't need to stasis through anything, I go with soul as my default.
If you're roflstomping to your little black hearts content and base with a gob of gold, get crown after leggings. It's rude.
I generally start hive for my first ability unless I can/need to pressure out of the gate, than mark. I generally think Mark offers the strongest start, but it's match dependant.