Thirteen skyscrapers apiece are chosen in 13 cities, where in each the top 13 floors, including the roof are made only accessible for 13 days to the members of the 13 teams.
The 13 floors are controlled (where control equates to the ability to grant or revoke access) by one ⅌ such that they are a different floor number in each of the 13 skyscrapers of a given city.
News could circulate that a new type of black mold was propagating through the stratosphere & infecting the tallest buildings worldwide. The parties could operate under the auspices of curing that.
That would also provide a cover for obscuring the windows.
Rooftop property is particularly coveted & each team has 13 rooftops across the 13 cities.
A collaborative map is used to delineate the purpose of different areas.