Yes, you do need VLAN segmentation to reduce your broadcast domains and per building is a good start. It doesn't make sense to have more ATVs than clients can see/list.
I understand too, having building WLAN Groups that use VLAN-override to assign VLAN to SSIDs,
your clients would be ok if they lose connection walking between buildings, as they would DHCP on the new building VLAN when they reconnect.
But, if they do remain associated going between building/AP groups, they would have/use their old VLAN IPs until they do a release/renew or purposely re-connect. You might use a short lease time or need to use different building SSIDs if the overlap is too much.
If you have many individual buildings on individual VLANs, you might use Bonjour Gateway to permit
ATV between the next to one another neighbor building VLANs as another alternative, so the users would be ok until they re-DHCP.