I’ve created a map with two buildings, but there’s no specific building ID or any clear way to select a buildings?
Hi Saurabh,
Welcome to the forum! This isn’t possible just yet, but is something we’re building (pun intended). 
Multi building support should be available in about a month from now. You’ll be able to group multiple buildings in the editor and then each building will be represented as a FloorStack in Mappedin JS.