Preferably find a casino with low security high profit, access doesn't matter.

Lure the guards out of the casino by being detected by cameras, when they run out setup the door block. I use the black couches from the lobby and just drag one around back before blocking the front door access.

Make sure doors are off of the doorways using a wrench before moving on to next part. AI opening the doors will move the couches and let them in/out.

Enter the casino by the roof and run down all of the stairs to the vault. unhook the painting in the office and use the key card behind it to unlock the vault.

Drag all your valuable loot out to the roof and throw to your car. stack it all up and make a good profit.

If done correctly police will not be called in and guards have no access inside the building, civilians in the building also have no way out after blockers are set up.