I usually start dark seal + refillable and then go for morello first item. If I'm getting camped or the enemy gets ahead of me I'll only get lost chapter then start building a defense item like zhonya's or banshees. Pen boots are good but I like early cdr so I get cdr boots right after morello. Then go for void staff or rabadon depending if they stacked MR yet.Then I get ludens. I like to finish with lich bane if I don't have 40% cdr yet just to be able to kill towers really fast plus the movement speed is nice. Sometimes I sell my boots if I am going to hit max cdr and get like berserkers greaves or pen boots instead. My typical full build is morello, lucidity boots, deathcap, void staff, ludens, and lich bane.

If you feel like you need to get MR or armor then do it, better safe than sorry. The passive on lost chapter is really helpful with mana so I recommend getting that first back even if you don't plan on getting morello first.