This mission is a hit on Enzo Bonelli, the contractor who locked down the Mile High Club skyscraper site and runs it on graft.
Gold Coast Development, the builder getting crushed by Bonelli's crooked firm, is the stock that benefits.
When Enzo Bonelli dies, Gold Coast's contracts and value spike. We buy Gold Coast before the mission and sell the high.
You fight armed guards from the ground floor to the roof, then you have to kill a helicopter — show up fully kitted.
Buy an RPG (rocket launcher) or Homing Launcher, Railgun if you can: it's the gold-medal tool and the mission-winner. Bonelli tries to leave the roof in a Buzzard; you need one shot to knock it out of the sky.
Heavy Sniper & Assault Rifle: your mains while the lift climbs — pick off distant snipers and the guards pouring in.
Super Heavy Armor & snacks: the site is wide open, so you will get hit. Max the armor bar at Ammu-Nation and stuff the inventory with EgoChaser and other store snacks for health.