I think I answered my own question. There would be no need to request a new IP if all the client VLAN's are availabe on each AP in the ap group for all the buildings.
So, I think my question should be how can I have 3,000 clients roam between 3 different buildings with 3 different L3 client VLAN's allowing 1,000 IP's per VLAN?
All AP's will be in the same ap group with the same WLAN profiles.
Would I have to use VLAN pooling in order not to run out of IP's per VLAN, keep the broadcast domains broken up between the client VLAN's, and to prevent any unecessary DHCP request? Or are there other options?