Hi Dipesh,
Try this:
1: Create WLAN Groups for each building
2: Create AP groups for each building
3: Create a SSID for each building:
WLAN should be named different for each building, but the ESSID can be the same. ESSID is what the client sees 'on the air'.
4: Assign the WLAN to the WLAN Group for the building, and assign that WG to the AP Group.
5: Assign AP's in each build to the AP group for that building
Test if it works.. I have not tried it, but in theory it should.
If you do this, just to keep DHCP ranges down, it might be easier to look into Dynamic VLAN's