Think of every program you have in place regarding your current building, and determine which programs fit the new one. Off hand, everything relating to pest control, warehouse handling, shipping/receiving, food defense, recall management, warehouse sanitation, GMP's (lighter version if only warehousing), all of those programs need to be modified to account for the new building.
Your Scope document that defines to SQF where you operate also needs to be updated to reflect the new building. This will include updating general maps, trash handling, people traffic maps, product flow maps, etc.
I've never had to handle the addition of a new building, but I think it would be appropriate to contact your CB to let them know you are adding a new building and want to schedule an audit for just that building (as it is an update to your process). They'd likely schedule the audit to have a few months worth of your monitoring records available for that new building.