What Jakob said.
I would add that you need to make sure there is no coverage overlap between your buildings. When clients roam from one AP to another on the same SSID, many clients will not send a DHCP request. If a client roams from AP A in building A on subnet A, to AP B in building B on subnet B, the client is suddenly in the wrong subnet and will lose IP connectivity.
If the distance between A and B is far enough that the client will have to disconnect from A before connecting to B later, you'll be fine.
If there IS overlap, either use different SSIDs, or use a single SSID and enable Tunnel mode, this way all the traffic will egress to the LAN at the ZD's port/VLAN.