Franklin has tailed the architect to the Mile High Club construction site is Los Santos.
Follow the architect
Switch to Franklin following the mission Reuniting the Family to begin this mission. Franklin has tailed the architect to a building site. Follow him through the construction site, ensuring that the architect doesn't spot you.
Make the architect give his suitcase
When prompted, make the architect give up his suitcase by having Franklin point a gun at him and holding him up (or killing him).
Leave the construction site
Once you have the suitcase, leave the construction site the same way you came in. If you didn't incapacitate the architect, you'll attain a wanted level.
Go to the clothing factory
Lose the cops if applicable, and go to the clothing factory and go up to Lester's office, where he'll run through the options and the heist plans..
Choose the heist approach
Select the heist approach for the FIB raid; either Rooftop, or Firetruck.
Choose your crew
Select your preferred crew to complete the mission.
Tip! If you've selected the rooftop approach, you can safely choose the crew members with the lowest cut percentage as nobody will die.
Quick Getaway - Leave the construction site within 45 seconds.