What is a realistic way to minimize inter-controller roaming in a large multibuilding campus?

Placing each building's controllers in a separate mobility group localizes roaming to within that group, so clients associated to a building's APs perform intra-mobility-group roaming rather than spanning controllers across all buildings. This is the standard Cisco design recommendation for large campuses to contain inter-controller roaming within defined architectural boundaries.

Joining all APs campus-wide to a single controller is not realistic or scalable for a large multi-building deployment, and creates a critical single point of failure.

Having all APs in a building join the same controller reduces intra-building inter-controller roaming but does not address the campus-wide mobility group architecture needed to contain roaming across buildings.

Load balancing APs across multiple controllers per building would increase inter-controller roaming events because clients within the same building would move between different controllers more frequently.